applied sciences

Article 2-D Seismic Response Analysis of a Slope in the Tyrrhenian Area ()

Antonio Cavallaro 1,* , Antonio Ferraro 2, Salvatore Grasso 2 and Antonio Puccia 2

1 CNR—ISPC National Research Council—Institute of Heritage Science, 95124 , Italy 2 Department of and Architecture, University of Catania, 95125 Catania, Italy; [email protected] (A.F.); [email protected] (S.G.); [email protected] (A.P.) * Correspondence: [email protected]

Abstract: The area is located in the Tyrrhenian north-eastern sector of (Italy). Starting in 2010, attention focused on the study of phenomena that occurred in this area, which caused significant economic damage to buildings and infrastructures and loss of productive activities. The site is characterized by geotechnical, geological and morphological heterogeneity, and for this reason the site is particularly prone to seismic topographic amplification effects. In this paper, the authors carried out numerical studies focused on the topographic seismic effect evaluation concerning the slope affected by the phenomena. For this site, geotechnical characterization was available concerning both in-situ and laboratory tests; , , down-hole tests, multichannel analysis of surface waves tests, seismic tomographies and inclinometer measurements were carried out. Furthermore, 1-D and 2-D local seismic response analyses were carried out by using different synthetic seismograms related to the of and Reggio on 28 December  1908. The results of the numerical analyses are presented in terms of response seismograms and  response spectra at the surface. Citation: Cavallaro, A.; Ferraro, A.; Grasso, S.; Puccia, A. 2-D Seismic Keywords: topographic effects; seismic response analysis; landslides; geotechnical characterization; Response Analysis of a Slope in the Tyrrhenian area Tyrrhenian Area (Italy). Appl. Sci. 2021, 11, 3180. https://doi.org/ 10.3390/app11073180 1. Introduction Academic Editors: Jong Wan Hu and The effects of the and geological conditions on seismic waves have been Antonio Cavallaro studied by many authors from the second half of the last century. The observation of the most important shows that the presence of topographic irregularities can Received: 20 December 2020 significantly modify the consequences of the seismic input motion; so much so that even Accepted: 26 March 2021 Published: 2 April 2021 the European Code [1] takes into account the modification of the seismic action due to topography through a topographical amplification factor.

Publisher’s Note: MDPI stays neutral Among the most important experiences that must be remembered include the study with regard to jurisdictional claims in on the Pacoima Dam in San Fernando Valley, California [2,3], and also the study on the published maps and institutional affil- Pacoima Canyon, which confirmed the very important role of topographic amplification iations. on landslide triggering [4]. In the recent past, the 1999 Athens Earthquake caused heavy damage on the eastern bank of the Kifissos River canyon and inspired the study on the topographic aggravation factor [5]. This paper is focused on the study of the local seismic amplification for a slope located in the Tyrrhenian north-eastern part of Sicily (Italy), carried out through 2-D numerical Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. analyses, to determine the topographical contribution on the ground acceleration [6–9]. This article is an open access article As is known, the local seismic response is significantly influenced by stratigraphic het- distributed under the terms and erogeneity and by morphological irregularities. The surface morphology is relevant on conditions of the Creative Commons the seismic amplification of the site as evidenced by the structural damages detected in Attribution (CC BY) license (https:// correspondence of morphological elements, such as the slopes, the escarpments and the creativecommons.org/licenses/by/ canyons. From the geotechnical point of view, the topographical amplification involves the 4.0/). evaluation of the seismic risk for the historical sites built on reliefs, but also for

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amplification involves the evaluation of the seismic risk for the historical sites built on reliefs,and important but also works for earthworks as bridges, dams,and impo naturalrtant and works artificial as bridges, slopes. Thedams, Italian natural Building and artificialCode (NTC slopes. 2018) The [10 ]Italian allows Building for the evaluation Code (NTC of 2018) topographic [10] allows amplification for the evaluation using a sim- of topographicplified method amplification based on theusing use a ofsimplified the topographic method based amplification on the use coefficient of the topographic ST, which amplificationvaries from a minimumcoefficient valueST, which of 1.0 varies to a maximum from a minimu value ofm 1.4.value However, of 1.0 to it a is maximum important valueto consider of 1.4. thatHowever, the values it is important suggested to by co NTCnsider 2018 that [10 the] are values referring suggested to general by NTC and 2018 not [10]particular are referring configurations to general and provideand not numerical particular values configurations that in some and cases provide may notnumerical be com- valuespletely realistic.that in some This workcases concerns may not the be determination completely ofrealistic. topographic This amplificationwork concerns factors the determinationthat could influence of topographic the slope amplification response in thefact caseors that of seismiccould influence events. Thethe slope topographical response inamplification the case of factors seismic were events. therefore The calculatedtopographical with 2-Damplification numerical modelsfactors andwere the therefore relative calculatedvalues obtained with 2-D from numerical the analyses models were and compared the relative with values the values obtained provided from by the the analyses Italian wereBuilding compared Code. with the values provided by the Italian Building Code. TheThe study study area area is is a a portion portion of of the the Caronia Caronia Municipality Municipality (Figure (Figure 1),1), where where in in 2010 2010 a non-coseismala non-coseismal landslide landslide affected affected the the southern southern part part of ofthe the town town and and caused caused damages damages to urbanizedto urbanized areas areas and and infrastructures; infrastructures; in inaddition, addition, about about 120 120 inhabitants inhabitants in in an an area area of approximatelyapproximately 50 hectares were evacuated.

FigureFigure 1. ViewView of the study area with map of the involvedinvolved locations during the 1908 earthquake.

2.2. Site Site Characterization Characterization 2.1.2.1. Seismicity Seismicity of of the the Study Study Area Area TheThe northern northern part part of of Sicily, Sicily, in front of the where Caronia is located, isis a a place of frequent, intense and deepdeep seismicityseismicity [[11].11]. This peculiarity attracted many seismologists,seismologists, explaining explaining the the large large number number of of papers dealing with it [12,13]. [12,13]. The area is prone to high seismic risk, and in the coastalcoastal part,part, toto highhigh tsunamitsunami risk.risk. The strongest historicalhistorical earthquake earthquake recorded recorded in in the area is also the strongest Italian earthquake, which tooktook place place in in the Messina Strait on 28 DecemberDecember 1908, causing an estimated 60,000 to 120,000 fatalities and the destruction of Messina, and many other cities in CalabriaCalabria and and Sicily. The 1908 earthquake, which was felt strongly in Sicily and Calabria (both(both regions of southern Ital Italy),y), was caused by normal faulting in the Messina Strait startingstarting at 05:20 a.m. on on 28 28 December December and lasting about 30 s. The The earthquake was also felt inin the the middle middle Italy Italy regions regions of of Campania Campania and Molise, as as on the Island (south ofof Sicily). TheThe shorelines of of Messina Messina and and Reggio Reggio Calabria Calabria were were stricken stricken by by up up to to 12 12 m m waves, completingcompleting the the devastation and and displacing a a large quantity of rubble from collapsed buildings.buildings. AsAs aa consequence consequence of theof disaster,the disaster, in the in areas the all areas communications all communications were disrupted were disruptedand rescue and operations rescue operations began right began from right the from sea thanksthe sea tothanks the presence to the presence of English of English ships shipsfirst and first then and also then Russian also Russian ships to ships give to immediate give immediate aide to theaide populations. to the populations. The medical The medicalofficers ofofficers the Royal of the Navy Royal and Navy the and Baltic the Guard-Marine Baltic Guard-Marine gave the gave first the medical first medical aid to aid the tovictims the victims [14]. [14]. Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 24 Appl. Sci. 2021, 11, 3180 3 of 23

Due to poor quality of construction and construction materials, the damage in MessinaDue and to poor Reggio quality Calabria of construction was very andstrong construction and contributed materials, to delivering the damage the in Messinacoup de graceand Reggio in the same Calabria areas was that very had strong already and suffer contributeded seismic to deliveringevents in th thee previous coup de 15 grace years, in suchthe same as the areas 1894, that 1905 had and already 1907 southern suffered seismicCalabria events earthquakes, in the previous all characterized 15 years, by such M ase > 6the [15]. 1894, Historic 1905 andrecords 1907 also southern report Calabriathat the Ionian earthquakes, Islands alloff characterizedthe west coast by of MGreecee > 6 [and15]. otherHistoric countries records such also as report Albania that an thed IonianMontenegro Islands felt off the the earthquake. west coast of Greece and other countriesThe area such of as the Albania Messina and Strait Montenegro is located felt midway the earthquake. of the Calabrian Arc, one of the most seismicallyThe area active of the areas Messina in StraitItalian is locatedand Me midwayditerranean of the Calabrianthat had Arc,been one stricken of the most by earthquakesseismically active several areas times in Italian in the and past, Mediterranean but not as strong that had as the been earthquake stricken by of earthquakes December 1908.several Figure times 2 inshows the past, the intensity but not as pattern strong for as the the 1908 earthquake earthquake of December [16]. Between 1908. theFigure main2 historicalshows the seismic intensity events pattern with for M thee > 19085.5, earthquakethe 31 August [16 ].853 Between and the the 6 mainFebruary historical 1783 seismic events with M > 5.5, the 31 August 853 and the 6 February 1783 earthquakes need earthquakes need to ebe mentioned, respectively, with I0 IX-X and I0 VIII-IX [17]. The to be mentioned, respectively, with I IX-X and I VIII-IX [17]. The historical records also historical records also report two events,0 presumably0 significant, in 91 B.C. (I0 IX-X) and report two events, presumably significant, in 91 B.C. (I IX-X) and 361 A.D. (I X). 361 A.D. (I0 X). 0 0

FigureFigure 2. 2.IntensityIntensity pattern pattern of of thethe 19081908 earthquake earthquake (after (after Mercalli, Mercalli, [16]). [16]). The dashed The dashed area suffered area su theffered strongest the groundstrongest shaking. ground shaking. 2.2. Geological Aspects 2.2. Geological Aspects The eastern sector of the Nebrodi Mountains (NE Sicily), a part of the Apennines- MaghrebianThe eastern orogenic sector , of the isNebrodi characterized Mountains by a (NE high Sicily), landslide a part hazard of the [ 18Apennines-,19]. The Maghrebianstudy area is orogenic characterized chain, is by characterized three different by a geological high landslide units hazard (Tardorogene [18,19]. The covering, study areaSicilide is characterized complex and Panormideby three different complex), geol accordingogical units to the (Tardorogene Geological Map covering, of the MessinaSicilide complexProvince, and as shown Panormide in Figure complex),3. according to the Geological Map of the Messina Province,The featuresas shown of in the Figure geological 3. units are reported in the following: The features of the geological units are reported in the following: (a) Tardorogene coverings unit—Reitano flysch: alternation of micaceous sandstones, of (a) Tardorogeneyellowish or gray-browncoverings unit—Reitano color, with intercalations flysch: alternation of grayish of micaceous or greenish sandstones, marly clays of yellowish or gray-brown color, with intercalations of grayish or greenish marly clays (Ma and Mas in the geological map). (b) (MaSicilide and complex—UpperMas in the geological scaly map). clays unit: marly clays and gray-blackish clayey marl (b) Sicilidewith decimetric complex—Upper levels of scaly gray clays marly unit: limestone marly clays and and grayish gray-blackish calcarenite clayey (Cc in marl the withgeological decimetric map); levels Salici of Mount—Castelli gray marly limestone Mount unit: and numidicgrayish calcarenite flysch, blackish (Cc in shafts the geological(OM in the map); geological Salici map)Mount—Castelli passing upwards Mount tounit: an alternationnumidic flysch, of brown blackish clays shafts and (OMyellowish in the quartz geological arenites map) with passing local marlyupwards limestone to an alternation and marl. of brown clays and (c) yellowishPanormide quartz complex—numidic arenites with local flysch, marly alternation limestone of and siliceous marl. argillites and quartz (c) Panormidearenites or quartzcomplex—numidic osyltites (Omi flysch, in the alternation geological map).of siliceous argillites and quartz arenites or quartz osyltites (Omi in the geological map). Appl. Sci. 2021, 11, 3180 4 of 23 Appl. Sci. 2021, 11, x FOR PEER REVIEW 4 of 24

InIn general, itit isis observed observed that that some some portions portions of of the the Reitano Reitano Flysch Flysch appear appear disarticulated disarticu- latedin the in outcrop, the outcrop, with fragmentedwith fragmented and fractured and fractured lithoid lithoid layers. layers.

Figure 3. Geological map of the study area [[20].20].

2.3. Investigation Investigation Program Program an andd Geotechnical Properties The Regional Regional Department of th thee Civil Defense put in many efforts in terms of studies and analyses thatthat obtainedobtained precious precious information information for for a detaileda detailed geotechnical geotechnical characterization characteriza- tionof the of Caroniathe Caronia area area [21]. [21]. The static and dynamicdynamic geotechnicalgeotechnical characterization characterization of of soils in in the the Contrada Contrada Lineri Lineri of ofCaronia Caronia was was performed performed within within an investigationan investigation test test site site with with a surface a surface of about of about 13 hectares; 13 hec- tares;Figure Figure4 shows 4 shows the layout the layout of test of sites test with sites thewith location the location of geotechnical of geotechnical boreholes boreholes and andpiezometers. piezometers. The study area reached a maximum depth of 30 m. Laboratory tests (moisture content; soil unit weight; specific gravity; grain size analysis; ; direct test) were performed on undisturbed samples [22]. To evaluate the geotechnical characteristics of soils, the following in situ and laboratory tests were performed in the area: n. 11 Boreholes, n. 10 Piezometers, n. 5 Inclinometric Mea- surements, n. 3 Down-Hole tests (DHT), n. 7 Seismic Tomography Tests, n. 2 Multichannel Analysis of Surface Waves (MASW), n. 12 Direct Shear Tests (DST). Appl. Sci. 2021, 11, 3180 5 of 23 Appl. Sci. 2021, 11, x FOR PEER REVIEW 5 of 24

FigureFigure 4. 4. LayoutLayout of of test test sites sites with with the the location location of of geotechnical geotechnical boreholes boreholes and piezometers.

TheBased study on ofarea the reached data available a maximum from depth boreholes of 30 (Table m. Laboratory1), soil profiles tests (moisture of the ground con- tent;beneath soil theunit Caronia weight; testspecific sites gravity; could be grain designed. size analysis; Summarizing Atterberg the limits; direct results, shear it test)is possible were performed to define on four undisturbed soil classes, samples namely: [22]. plastic structureless clays, brown color structurelessTo evaluate clays, the gray geotechnical color structureless characteristics clays of and soils, argillites. the following The water in situ level and was labora- in the toryrange tests 8.30–11.20 were performed m. in the area: n. 11 Boreholes, n. 10 Piezometers, n. 5 Inclinometric Measurements, n. 3 Down-Hole tests (DHT), n. 7 Seismic Tomography Tests, n. 2 Multi- Table 1. channel Analysis of SurfaceSoil profile Waves for Caronia (MASW), area. n. 12 Direct Shear Tests (DST). D Based on of the data available from boreholes (Table 1), soil profiles of Vthe ground Borehole Soil Profile S [m] beneath the Caronia test sites could be designed. Summarizing the borehole[m/s] results, it is BH105 0.00–4.00possible Debris: to define conglomerate four soil screed, classes, boulders namely: and plastic chaotic structureless material. clays, brown <260 color struc- tureless clays, gray color structureless clays and argillites. The water level was in the range Tobacco brown clays, to the touch plastic and from medium 8.30–11.20 m. consistent to consistent in the lower part (10.50–15.50 m); at times BH105 4.00–15.50 <350 Thethere stratigraphic are clay levels; columns overall, whenwere ,obtained they present directly themselves by the study with of topographical pro- files. ferrous,This was rust-colored done by andtrying alternatively to predict gray as alterations.accurately as possible what the soil profile lookedDark like gray beneath with the verysurface consistent from the sections, information alternating available with from the stratigraphic col- >450 BH105 15.50–31.00umns,fractured linking andcorresponding flattened layers; strata moreover, with ne thereighboring are rare stratigraphic levels of clay columns where possi- <600 ble. Oncewith plasticeach stratum behavior andwas dark completed, color. the corresponding lithological design was as- BH3 0.00–4.00signed Plastic (Figure structureless 5). clays (landslide debris). <260 Chaotic structureless clay with occasional compact clay levels of BH3 4.00–6.00 Table 1. Soil profile for Caronia area. <350 brown color with plastic consistency and poor characteristics. D Chaotic structureless clay with occasional compact clay levels of gray >350 VS BoreholeBH3 6.00–15.50 Soil Profile [m] color with plastic consistency and mediocre characteristics. <450 [m/s] BH105 0.00–4.00 Debris:Argillites conglomerate with lytic tracts scre anded, sub-vertical boulders and fractures, chaotic dark material. gray or >450 <260 BH3 15.50–31.00 Tobaccoblackish brown in color clays with mediocre, to the touch characteristics. plastic and from medium consistent to<600 where: D = Depth, V consistent= Shear Wave in Velocity the lower and BH105part (10.50–15.5 or BH3 = Boreholes0 m); whereat times the profilesthere are were clay taken. levels; BH105 4.00–15.50 S <350 overall, when cut, they present themselves with ferrous, rust-colored and alternatively gray alterations. Appl. Sci. 2021, 11, x FOR PEER REVIEW 6 of 24

Dark gray clay with very consistent sections, alternating with fractured >450 BH105 15.50–31.00 and flattened layers; moreover, there are rare levels of clay with plastic be- <600 Appl. Sci. 2021, 11, 3180 havior and dark color. 6 of 23 BH3 0.00–4.00 Plastic structureless clays (landslide debris). <260 Chaotic structureless clay with occasional compact clay levels of brown BH3 4.00–6.00 <350 colorThe stratigraphicwith plastic consistency columns were and poor obtained characteristics. directly by the study of topographical profiles.Chaotic This structureless was done by clay trying with to occasional predict as accuratelycompact clay as possiblelevels of whatgray color the soil >350 profile BH3 6.00–15.50 lookedwith like plastic beneath consistency the surface and mediocre from the characteristics. information available from the stratigraphic<450 columns,Argillites linking with corresponding lytic tracts and strata sub-vertical with neighboring fractures, dark stratigraphic gray or blackish columns >450 where BH3 15.50–31.00 possible.in color Once with each mediocre stratum characteristics. was completed, the corresponding lithological design<600 was Where: D = Depth, VS = Shearassigned Wave Velocity (Figure and5). BH105 or BH3 = Boreholes where the profiles were taken.

FigureFigure 5.5. Soil profilesprofiles ofof S105S105 andand S3S3 boreholes.boreholes.

Based on thethe laboratorylaboratory tests,tests, thethe typicaltypical rangerange ofof physicalphysical characteristics,characteristics, indexindex properties andand strengthstrength parametersparameters ofof thethe depositsdeposits mainlymainly encounteredencountered inin thesethese areasareas areare reported inin TablesTables2 2 and and3 .3.

Table 2.2. MechanicalMechanical characteristicscharacteristics forfor CaroniaCaronia area.area.

D D γ γ Wn Wn WL WL WP WP PI PI CICI AIAI SiteSite 3 [m] [m] [kN/m[kN/m3] ] [%] [%] [%] [%] [%] [%] [%] [%] [%][%] [%][%] BH2CI1BH2CI1 2.50–3.00 2.50–3.00 19.81 19.81 12.54 12.54 34.17 34.17 11.98 11.98 22.19 22.19 0.97 0.97 1.07 1.07 BH3CI1BH3CI1 2.50–3.00 2.50–3.00 19.71 19.71 26.21 26.21 31.78 31.78 22.71 22.71 9.07 9.07 1.58 1.58 0.34 0.34 BH3CI2 6.00–6.40 19.61 22.65 37.63 19.74 17.89 0.97 0.44 BH3CI2 6.00–6.40 19.61 22.65 37.63 19.74 17.89 0.97 0.44 BH4CI1 7.30–7.60 18.24 15.78 53.27 20.20 33.07 0.99 0.64 BH4CI1BH4CI2 7.30–7.60 10.70–11.00 18.24 19.22 15.78 24.45 53.27 22.58 20.20 13.42 33.07 9.16 0.99 1.29 0.64 0.52 BH4CI2BH5CI1 10.70–11.00 12.00–12.45 19.22 19.12 24.45 26.35 22.58 48.56 13.42 20.06 9.16 28.50 1.29 0.96 0.52 0.48 BH102-CM1 4.20–450 19.71 14.12 38.00 17.00 21.00 1.14 0.87 BH2CI1 2.50–3.00 19.81 12.54 34.17 11.98 22.19 0.97 1.07 BH3CI1 2.50–3.00 19.71 26.21 31.78 22.71 9.07 1.58 0.34 BH3CI2 6.00–6.40 19.61 22.65 37.63 19.74 17.89 0.97 0.44 BH4CI1 7.30–7.60 18.24 15.78 53.27 20.20 33.07 0.99 0.64 BH4CI2 10.70–11.00 19.22 24.45 22.58 13.42 9.16 1.29 0.52

where: D = Depth, γ = Total Unit Weight, Wn = , WL = Liquid Limit, WP = Plastic Limit, PI = Plasticity Index, CI = Consistence Index and AI = Activity Index. Appl. Sci. 2021, 11, x FOR PEER REVIEW 7 of 24

BH5CI1 12.00–12.45 19.12 26.35 48.56 20.06 28.50 0.96 0.48 BH102-CM1 4.20–450 19.71 14.12 38.00 17.00 21.00 1.14 0.87 BH2CI1 2.50–3.00 19.81 12.54 34.17 11.98 22.19 0.97 1.07 BH3CI1 2.50–3.00 19.71 26.21 31.78 22.71 9.07 1.58 0.34 BH3CI2 6.00–6.40 19.61 22.65 37.63 19.74 17.89 0.97 0.44 BH4CI1 7.30–7.60 18.24 15.78 53.27 20.20 33.07 0.99 0.64 BH4CI2 10.70–11.00 19.22 24.45 22.58 13.42 9.16 1.29 0.52 where: D = Depth, γ = Total Unit Weight, Wn = Water Content, WL = Liquid Limit, WP = Plastic Limit, PI = Plasticity Index, CI = Consistence Index and AI = Activity Index.

Appl. Sci. 2021, 11, 3180 Table 3. Mechanical characteristics for Caronia area. 7 of 23

D Sr c’ φ‘ Site e n [m] [%] [kPa] [°] BH2CI1 2.50–3.00 0.51 0.34 66.58 4.88 31.6 BH3CI1 2.50–3.00 0.66 0.40 69.89 5.86 27.6 Table 3. Mechanical characteristics for Caronia area. BH3CI2 6.00–6.40 0.66 0.40 81.96 6.93 23.4 BH4CI1 7.30–7.60D 0.57 0.36 95.58Sr 19.95c’ 28.1ϕ‘ Site e n ◦ BH4CI2 10.70–11.00[m] 0.43 0.30 67.06[%] [kPa]21.73 15.8[ ] BH5CI1BH2CI1 12.00–12.45 2.50–3.00 0.510.74 0.340.43 78.9666.58 4.882.41 31.616.0 BH102-CM1BH3CI1 2.50–3.004.20–450 0.660.52 0.400.34 73.1269.89 33.20 5.86 27.6 21 BH3CI2 6.00–6.40 0.66 0.40 81.96 6.93 23.4 BH2CI1BH4CI1 2.50–3.00 7.30–7.60 0.570.44 0.360.30 67.0295.58 20.3019.95 28.1 22 BH3CI1BH4CI2 10.70–11.002.50–3.00 0.430.49 0.300.33 78.8867.06 36.5021.73 15.8 30 BH3CI2BH5CI1 12.00–12.456.00–6.40 0.740.44 0.430.31 85.0778.96 51.80 2.41 16.0 22 BH102-CM1BH4CI1 7.30–7.60 4.20–450 0.520.39 0.340.28 73.3073.12 34.0033.20 2120 BH2CI1 2.50–3.00 0.44 0.30 67.02 20.30 22 BH4CI2 10.70–11.00 0.35 0.26 85.63 23.20 21 BH3CI1 2.50–3.00 0.49 0.33 78.88 36.50 30 BH3CI2where: D = Depth, 6.00–6.40 e = , n = 0.44, Sr = Degree 0.31 of Saturation, c’ 85.07= and φ‘ 51.80 = Effective angle 22 BH4CI1from Direct Shear 7.30–7.60Test (DST). 0.39 0.28 73.30 34.00 20 BH4CI2 10.70–11.00 0.35 0.26 85.63 23.20 21 n where: D = Depth, e = Void Ratio, nThe = Porosity, value Sr(Figure = Degree 6) of of Saturation, the natural c’ = Cohesion moisture and contentϕ‘ = Effective w prevalently friction angle fromranged Direct between Shear Test (DST). 11–26%, while characteristic values for e (void ratio) ranged between 0.35 and 0.74 for the Caronia test site. Regarding strength parameters of the deposits mainly (Table 3) encountered in this The value (Figure6) of the natural moisture content w n prevalently ranged between 11–26%,area, c’ from while DST characteristic ranged betw valueseen for2.41kPa e (void and ratio) 51.8kPa ranged while between φ‘ from 0.35 DST and 0.74ranged for thebe- Caroniatween 15.8° test and site. 31.6°.

Figure 6.6. Index propertiesproperties ofof CaroniaCaronia area,area, where:where: DD == Depth,Depth, CFCF == ClayClay Fraction,Fraction, WWPP = Plastic Limit, Wn = Water Water Content, WWLL = Liquid Limit, PI = Plasticity Plasticity Index, Index, γγ == Total Total Unit Unit Weight Weight and e = Void Void Ratio.

Regarding strength parameters of the deposits mainly (Table3) encountered in this area, c’ from DST ranged between 2.41kPa and 51.8kPa while ϕ‘ from DST ranged between 15.8◦ and 31.6◦. It was also possible to evaluate the small strain shear modulus in the Caronia area by means of the following seismic tests based on Down Hole (DH). In Figure7, the shear and compression wave velocities are shown against depth. The shear Vs and compression Vp wave velocities gradually increased with depth. At the depth of about 25–30 m, there was a rapid increase in velocities due to the presence of fractured argillite. In Figure8, the dynamic Poisson ratio ( ν) variation with depth, obtained from the Down-Hole (DH) test, is plotted to show site characteristics. It is shown that the values oscillate around 0.03–0.48 for DH. Appl. Sci. 2021, 11, x FOR PEER REVIEW 8 of 24

Appl. Sci. 2021, 11, x FOR PEER REVIEW 8 of 24

It was also possible to evaluate the small strain shear modulus in the Caronia area by means of the following seismic tests based on Down Hole (DH). In Figure 7, the shear and compressionIt was also wave possible velocities to evaluate are the shown small strain against shear modulusdepth. in the Caronia area by means of the following seismic tests based on Down Hole (DH). In Figure 7, the shear and The shear Vs and compression Vp wave velocities gradually increased with depth. At Appl. Sci. 2021, 11, 3180 compression wave velocities are shown against depth. 8 of 23 the depthThe shear of about Vs and 25–30 compression m, there Vp wave was velocities a rapid gradually increase increased in velocities with depth. due At to the presence of fracturedthe depth ofargillite. about 25–30 m, there was a rapid increase in velocities due to the presence of fractured argillite.

V [m/s] V [m/s] V [m/s] V [m/s] V [m/s] V [m/s] 00 500 500 1000 1000 1500 00 1000 1000 2000 2000 3000 30000 5000 1000 500 1500 1000 1500 0 0 0 0 0 0 VsVs - -DH1 DH1 Vs - DH2 Vs - DH2 Vs - DH3 Vs - DH3 Vp - DH1 Vp - DH2 Vp - DH3 5 5 Vp - DH1 5 5 Vp - DH2 5 5 Vp - DH3 10 10 10 10 10 10 15 15 15 D [m] D

D [m] D 15 15 [m] D 15 20 20 20 D [m] D D [m] D 20 25 25[m] D 20 25 20

30 25 30 3025 25 CARONIA CARONIA CARONIA 35 Borehole BH2 35 Borehole BH5 35 Borehole BH3 30 30 30 FigureCARONIA 7. Vs and Vp from down-hole tests in CaroniaCARONIA area, where: Vs = Shear wave velocity and VCARONIAp = Compression wave velocity.35 Borehole BH2 35 Borehole BH5 35 Borehole BH3

In Figure 8, the dynamic Poisson ratio (ν) variation with depth, obtained from the Figure 7. VVs sandand V Vp pfromfrom down-hole down-hole tests tests in inCaronia Caronia area, area, where: where: Vs = V Shears = Shear wave wave velocity velocity and V andp = Compression Vp = Compression wave Down-Hole (DH) test, is plotted to show site characteristics. It is shown that the values wave velocity. velocity. oscillate around 0.03–0.48 for DH.

In Figure 8, the dynamic Poissonν ratio (ν) variation with depth, obtained from the Down-Hole0.00 (DH) 0.10test, is plotted 0.20 to show 0.30 site characteristics. 0.40 It 0.50is shown that the values oscillate0 around 0.03–0.48 for DH. 5 ν 10 0.00 0.10 0.20 0.30 0.40 0.50 150

D [m] 20 CARONIA 5 DH 1 25 DH 2 10 DH 3 30

1535

FigureFigureD [m] 20 8.8. PoissonCARONIA ratio ratio from from down-hole down-hole tests. tests.

DH 1 25InIn Figure 9,9 the, the coefficient coefficient of earth of earthpressure pressure at rest Ko atvariation rest K witho variation depth, obtained with depth, obtained Appl. Sci. 2021, 11, x FOR PEER REVIEWfrom a Down-HoleDH (DH) 2 test, is plotted to show site characteristics. It is shown that9 ofapart 24 from a Down-Hole (DH) test, is plotted to show site characteristics. It is shown that apart from the top 5 m, theDH values3 oscillate around 0.07–0.93 from DH. from30 the top 5 m, the values oscillate around 0.07–0.93 from DH.

K 35 o 0.00 0.20 0.40 0.60 0.80 1.00 0 Figure 8. Poisson ratio from down-hole tests. DH 1 5 DH 2 DH 3 In Figure 9, the coefficient of earth pressure at rest Ko variation with depth, obtained 10 from a Down-Hole (DH) test, is plotted to show site characteristics. It is shown that apart from15 the top 5 m, the values oscillate around 0.07–0.93 from DH.

D [m] 20

25

30 CARONIA

35

FigureFigure 9. 9. TheThe coefficient coefficient of earth of pressure earth pressure at rest K0 atfrom rest down-hole Ko from tests. down-hole tests.

A comparison between the shear modulus values of Go obtained from in situ tests A comparison between the shear modulus values of Go obtained from in situ tests performedperformed on on the thearea area under under consideration consideration is shown in is Figure shown 10. inThe Figure down-hole 10. Thetests down-hole tests performed in the Caronia area show Go values increasing with depth. Very high values of Go were obtained for depths greater than 25 m in borehole 5. According to these data, it was possible to assume Go values oscillating around 50–1000 MPa.

Go [MPa] 0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 0

DH 1 - Borehole 2 5 DH 2 - Borehole 5 DH 3 - Borehole 3 10

15

D [m] 20

25

30

35

Figure 10. Shear modulus values of G0 from down-hole tests.

Figure 11 shows a particular cross-section with the geological and geotechnical infor- mation from which we note the presence of predominantly clayey material with Vs values included in the range 200–700 m/s. The borehole BH105 was performed along with the stable share of landslide cross-section, while the borehole BH3 was performed along with the unstable share of landslide cross-section. These two boreholes allow us to definition the geotechnical characteristics of the Caronia landslide. Appl. Sci. 2021, 11, x FOR PEER REVIEW 9 of 24

Ko 0.00 0.20 0.40 0.60 0.80 1.00 0 DH 1 5 DH 2 DH 3 10

15

D [m] 20

25

30 CARONIA

35 Appl. Sci. 2021, 11, 3180 9 of 23 Figure 9. The coefficient of earth pressure at rest K0 from down-hole tests.

A comparison between the shear modulus values of Go obtained from in situ tests performed on the area under consideration is shown in Figure 10. The down-hole tests performed in the Caronia area show G values increasing with depth. Very high values of performed in the Caronia area show Go values increasingo with depth. Very high values of GGo werewere obtained obtained for depths for depths greater greaterthan 25 m than in borehole 25 m in5. According borehole to 5. these According data, it to these data, it waswas possible possible to assume to assume Go values Go valuesoscillating oscillating around 50–1000 around MPa. 50–1000 MPa.

Go [MPa] 0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 0

DH 1 - Borehole 2 5 DH 2 - Borehole 5 DH 3 - Borehole 3 10

15

D [m] 20

25

30

35

FigureFigure 10. 10. ShearShear modulus modulus values valuesof G0 from of down-hole Go from down-holetests. tests.

FigureFigure 11 11shows shows a particular a particular cross-section cross-section with the geological with the and geological geotechnical and infor- geotechnical infor- mation from which we note the presence of predominantly clayey material with Vs values mationincluded fromin the whichrange 200–700 we note m/s. the The presence borehole BH105 of predominantly was performed clayey along with material the with Vs values includedstable share inof landslide the range cross-section, 200–700 m/s.while the The borehole borehole BH3 was BH105 performed was performedalong with along with the stablethe unstable share share of landslide of landslide cross-section, cross-section. These while two the boreholes borehole allow BH3 us to was definition performed along with Appl. Sci. 2021, 11, x FOR PEER REVIEWthethe geotechnical unstable share characteristics of landslide of the Caronia cross-section. landslide. These two boreholes allow us10 toof definition24

the geotechnical characteristics of the Caronia landslide.

FigureFigure 11. ParticularsParticulars of ofthe the cross-section. cross-section.

3. Site Response Analysis 3.1. Seismic Input Motion and Soil Dynamic Properties This work takes into specific consideration the site effects’ role on the predictable ground motions in the Caronia area. More precisely, when it comes to site effects, we gen- erally refer to the influence of the first 40–50 m of near-surface stratigraphy on the seismic response of the soil. Great importance is also given to the source and the path effects [23]. Seven different inputs were used, consisting of six synthetic seismograms related to the Messina and Reggio Calabria 1908 earthquake (Bottari et al. [24]; Tortorici et al. [25]; Amoruso et al. [26]; DISS Aspromonte Est; DISS Gioia Tauro; DISS Messina Strait) and one related to the 1693 Catania scenario earthquake [27–30]. The seismograms were scaled to the (Peak Ground Acceleration) PGA = 0.176 g provided by the Italian Code NTC 2018 for the site. Soil dynamic properties were also taken into account in the numerical analyses through the stiffness attenuation G/Go-γ and damping ratio evolution with strain D-γ curves [31] related to similar materials of the same area [32,33]. The dependency of the shear modulus and damping ratio on shear strain level was obtained by interpolating the experimental resonant column tests (RCT) data by Yokota et al.’s [34] equation to the experimental data points. For the Caronia area, the following equations were used: G(γ) 1 = + β (1) G o 1 αγ(%) to describe the shear modulus decay with shear strain level, in which G(γ) = strain de- pendent shear modulus, γ = shear strain and α, β = soil constants, with Appl. Sci. 2021, 11, 3180 10 of 23

3. Site Response Analysis 3.1. Seismic Input Motion and Soil Dynamic Properties This work takes into specific consideration the site effects’ role on the predictable ground motions in the Caronia area. More precisely, when it comes to site effects, we generally refer to the influence of the first 40–50 m of near-surface stratigraphy on the seismic response of the soil. Great importance is also given to the source and the path effects [23]. Seven different inputs were used, consisting of six synthetic seismograms related to the Messina and Reggio Calabria 1908 earthquake (Bottari et al. [24]; Tortorici et al. [25]; Amoruso et al. [26]; DISS Aspromonte Est; DISS Gioia Tauro; DISS Messina Strait) and one related to the 1693 Catania scenario earthquake [27–30]. The seismograms were scaled to the (Peak Ground Acceleration) PGA = 0.176 g provided by the Italian Code NTC 2018 for the site. Soil dynamic properties were also taken into account in the numerical analyses through the stiffness attenuation G/Go-γ and damping ratio evolution with strain D-γ curves [31] related to similar materials of the same area [32,33]. The dependency of the shear modulus and damping ratio on shear strain level was obtained by interpolating the experimental resonant column tests (RCT) data by Yokota et al.’s [34] equation to the experimental data points. For the Caronia area, the following equations were used:

G(γ) 1 = β (1) Go 1 + αγ(%)

to describe the shear modulus decay with shear strain level, in which G(γ) = strain depen- dent shear modulus, γ = shear strain and α, β = soil constants, with

 G(γ)  D(γ)(%) = η · exp −λ · (2) Go

to describe the inverse variation of damping ratio with respect to the normalized shear modulus, in which D(γ) = strain dependent damping ratio, γ = shear strain and η, λ = soil constants. The values of α, β and of η, λ are reported in Table4.

Table 4. Soil constants for Caronia area.

Soil α β η λ Debris 65 1.15 34.8 1.9 Brown Clay 20 0.87 19 2.3 Dark Gray Clay 7.5 0.897 90 4.5

3.2. Numerical Analyses To evaluate morphological and stratigraphic effects, 1-D and 2-D equivalent-linear site response analyses were performed. Several techniques were proposed for the assessment of these effects; by comparing the results from experimental estimates of local site amplifi- cation effects and numerical analyses, it was demonstrated that 1-D numerical modeling can underestimate the amplification of ground motion and cannot account for resonant frequencies every time [35]. In these cases, the use of 2-D numerical methods is almost essential to obtain a more realistic estimate of the seismic response [36]. The 1-D analyses were carried out in three vertical profiles extracted from the 2-D cross-section, located in this way: (1) the first behind the crest of the slope, (2) the second at the crest of the slope, (3) the third at a point downstream sufficiently far from the foot of the slope. Appl. Sci. 2021, 11, 3180 11 of 23

The 1-D analyses were performed by the EERA (Equivalent-Linear Earthquake Site Response Analysis) code [37] that permits performance of frequency domain analyses for equivalent linear stratified sub-soils. The same elaborations were also carried out through the QUAKE/W code to obtain a calibration of the two codes and be able to proceed subsequently with the 2-D analyses. A comparison of results from these two different codes is a good way of validating the formulation and implementation of the work. The EERA model was simulated in QUAKE/W as a column of elements where the base of the column is fixed. This has the effect of the earthquake motion being applied at the column base. The sides of the column are fixed in the vertical direction, which ensures that all the motion is in the horizontal direction only, an assumption inherent in the EERA 1-D formulation. The 2-D analyses were performed by the QUAKE/W [38] code based on a finite ele- ment formulation with a direct integration scheme in the time domain. “Direct integration” means no transformation of the equations into the frequency domain is required. Then, the motion equations are solved directly using a finite-difference time-stepping procedure. Appl. Sci. 2021, 11, x FOR PEER REVIEW Figure 12 shows the cross-section used for the finite element analyses; the three-surface12 of 24

points monitored by 1-D and 2-D analyses were also indicated in the same figure.

Figure 12. Cross-sectionCross-section and location of the three monitored points.

3.3. 1-D 1-D Analysis Analysis For complex geometries,geometries, itit isis veryvery important important to to perform perform dynamic dynamic analyses analyses by by different differ- entcodes, codes, and and in particularin particular through through 2-D 2-D codes codes that that can can catch catch some some aspects aspects thatthat 1-D1-D codes cannot catch. The 1-D analyses performed by EERA and QUAKE/WQUAKE/W codes, codes, for for the the seven inputs, show similar values of PGA for points points 1 1 and and 2 2 (behind (behind the the crest crest point point and and crest crest point) point) [39]. [39]. The following figuresfigures show show in in red red and and blue, blue, respectively, respectively, the the EERA EERA and and QUAKE/W QUAKE/W results re- sultsin terms in terms of acceleration of acceleration time historytime history and spectral and spectral acceleration. acceleration. In particular, In particular,Figures Figures 13–15 13–15show theshow 1-D the analysis 1-D analysis results results for the for Amoruso the Amoruso et al. [et26 al.] input, [26] input, and the and results the results have have been beensummarized summarized in the in Table the 5Table. Results 5. Results obtained obtained for points for points 1 and 21 showand 2 valuesshow values of the strati-of the stratigraphicgraphic soil amplification soil amplification factor factor of about of about 1.30 using 1.30 using the EERA the EERA code andcode of and about of about 1.20 using 1.20 usingthe QUAKE/W the QUAKE/W code. code. For point For point 3, there 3, there is no is significant no significant stratigraphic stratigraphic soil amplification. soil amplifica- tion. Table 6 shows, for the same points, the results of 1-D analysis carried out by the seis- mograms for the Bottari et al. [24], Tortorici et al. [25], DISS Messina Strait, DISS Gioia Tauro, DISS Aspromonte Est, and 1693 Catania Earthquake. Results obtained for points 1 and 2, show maximum values of the stratigraphic soil amplification factor of about 1.45 using EERA code and of about 1.50 using QUAKE/W code. While for point 3 results show a slight stratigraphic soil amplification of about 1.10. Appl. Sci. 2021, 11, 3180 12 of 23 Appl. Sci. 2021, 11, x FOR PEER REVIEW 13 of 24 Appl. Sci. 2021, 11, x FOR PEER REVIEW 13 of 24

FigureFigure 13.13. ComparisonComparison between between 1-D 1-D analyses analyses performe performedd by by Equivalent-Linear Equivalent-Linear Earthquake Earthquake Site Site Figure 13. Comparison between 1-D analyses performed by Equivalent-Linear Earthquake Site ResponseResponse AnalysisAnalysis (EERA) and QUAKE/W for for point point 1, 1, in in terms terms of of accelera accelerationtion time time history history and and Response Analysis (EERA) and QUAKE/W for point 1, in terms of acceleration time history and spectralspectral acceleration,acceleration, forfor thethe AmorusoAmoruso etet al.al. [[26]26] input.input. spectral acceleration, for the Amoruso et al. [26] input.

Figure 14. Comparison between 1-D analyses performed by EERA and QUAKE/W for point 2, in FigureFigureterms of 14.14. acceleration ComparisonComparison time between history 1-D and analyses spectral performeperformed acceleration,d by by forEERA EERA the andAmoruso and QUAKE/W QUAKE/W et al. [26] for for pointinput. point 2, 2,in in termsterms ofof accelerationacceleration timetime historyhistory andand spectralspectral acceleration,acceleration, forfor thethe AmorusoAmoruso etet al.al. [[26]26] input.input. Appl. Sci. 2021, 11, 3180 13 of 23 Appl. Sci. 2021, 11, x FOR PEER REVIEW 14 of 24

FigureFigure 15. ComparisonComparison between between 1-D 1-Danalyses analyses performe performedd by EERA by and EERA QUAKE/W and QUAKE/W for point 3, for in point 3, in terms of acceleration time history and spectral acceleration, for the Amoruso et al. [26] input. terms of acceleration time history and spectral acceleration, for the Amoruso et al. [26] input. Table 5. PGA (Peak Ground Acceleration) by 1-D analyses for the Amoruso et al. [26] input at Tablepoint 1, 5. 2PGA and 3. (Peak Ground Acceleration) by 1-D analyses for the Amoruso et al. [26] input at point 1, 2 and 3. PGAEERA PGAQUAKE/W 1-D

[g] [g] PGAEERA PGAQUAKE/W 1-D Point 1 0.228 [g] 0.207 [g] Point 2 0.228 0.207 Point 1 0.228 0.207 Point 3 0.168 0.141 Point 2 0.228 0.207 Point 3 0.168 0.141 Table 6. PGA by 1-D analyses for the Bottari et al. [24], Tortorici et al. [25], DISS Messina Strait, DISS Gioia Tauro, DISS Aspromonte Est, 1693 Catania earthquake inputs at point 1, 2 and 3. Table6 shows, for the same points, the results of 1-D analysis carried out by the Tortorici et al. [25] Bottari et al. [24] DISS Messina Strait seismograms for the Bottari et al. [24], Tortorici et al. [25], DISS Messina Strait, DISS Gioia PGA PGA PGA PGA PGA PGA Tauro, DISS Aspromonte Est, and 1693 Catania Earthquake. EERA QUAKE/W 1-D EERA QUAKE/W 1-D EERA QUAKE/W 1-D [g] [g] [g] [g] [g] [g] Table 6. PGA by 1-D analyses for the Bottari et al. [24], Tortorici et al. [25], DISS Messina Strait, DISS Gioia Tauro, DISS Point 1 0.208 0.193 0.208 0.156 0.195 0.269 Aspromonte Est, 1693 Catania earthquake inputs at point 1, 2 and 3. Point 2 0.208 0.193 0.208 0.156 0.195 0.269 Point 3 0.176Tortorici et al. [0.14725] 0.184 Bottari et al.0.152 [24 ]0.165 DISS Messina0.151 Strait DISS Gioia Tauro DISS Aspromonte Est 1693 Catania Earthquake PGA PGA PGA PGA PGA PGA PGA PGA PGA PGA PGA PGA EERA QUAKE/W 1-D EERA QUAKE/W 1-D EERA QUAKE/W 1-D [g]EERA QUAKE/W [g] 1-D EERA [g] QUAKE/W 1-D [g] EERA [g]QUAKE/W 1-D [g] [g] [g] [g] [g] [g] [g] Point 1 0.208 0.193 0.208 0.156 0.195 0.269 Point 1 0.257 0.203 0.206 0.266 0.179 0.142 Point 2 0.208 0.193 0.208 0.156 0.195 0.269 0.257 0.203 0.206 0.266 0.179 0.142 PointPoint 3 2 0.176 0.147 0.184 0.152 0.165 0.151 Point 3 0.202 0.157 0.181 0.167 0.154 0.117 DISS Gioia Tauro DISS Aspromonte Est 1693 Catania Earthquake PGA 3.4. 2-D AnalysisPGA PGA PGA PGA PGA EERA QUAKE/W 1-D EERA QUAKE/W 1-D EERA QUAKE/W 1-D [g] [g] [g] [g] [g] [g] Point 1 0.257 0.203 0.206 0.266 0.179 0.142 Point 2 0.257 0.203 0.206 0.266 0.179 0.142 Point 3 0.202 0.157 0.181 0.167 0.154 0.117 Appl. Sci. 2021, 11, 3180 14 of 23

Results obtained for points 1 and 2, show maximum values of the stratigraphic soil

Appl. Sci. 2021, 11, x FOR PEER REVIEWamplification factor of about 1.45 using EERA code and of about 1.50 using QUAKE/W15 of 24 code. While for point 3 results show a slight stratigraphic soil amplification of about 1.10.

3.4. 2-D Analysis InIn additionaddition to to 1-D 1-D results, results, a 2-D a analysis2-D analysis of the slopeof the was slope performed was performed using QUAKE/W using QUAKE/Wcode. The importance code. The importance of the comparison of the comparison for the same for casethe same study case between study 1-Dbetween and 2-D1-D andanalyses 2-D analyses is well known is well and known it plays and an it important plays an roleimportant not only role for not a sloping only for ground a sloping area groundbut, in general, area but, for in geometricgeneral, for irregularities. geometric irregularities. An example An is reported example by is Eltonreported et al. by [40 Elton] by etanalyzing al. [40] by the analyzing stability of the an stability earth dam of an affected earth bydam a seismic affected action. by a seismic Authors action. compared Authors two comparedmethods for two calculating methods thefor peakcalculating dynamic the shear peak stress dynamic that occursshear stress in embankments that occurs duringin em- bankmentsan earthquake during based an on earthq 1-D analysesuake based performed on 1-D usinganalyses the performed SHAKE code using [41 ]the and SHAKE on 2-D codeanalyses [41] carriedand on out2-D usinganalyses the carried FLUSH out code using [42]. the FLUSH code [42]. Furthermore, an accurate evaluation of the PGA also plays a very important role in slope stability in seismic conditions. In fact, the influence influence of the PGA on the identification identification of the critical slipslip surfacesurface underunder seismic seismic loading, loading, and, and, consequently, consequently, on on the the safety safety factor factor of ofthe the slope, slope, is wellis well known. known. In In addition, addition, the th knowledgee knowledge of of the the response response time time history history and and of ofthe the PGA PGA can can be verybe very helpful helpful in the in studythe study of permanent of permanent displacements, displacements, as recently as recently reported re- portedby Ji at by al. Ji [43 at,44 al.]. [43,44]. The followingfollowing figures figures show show in red, in bluered, andblue green, and respectively, green, respectively, the EERA, QUAKE/Wthe EERA, QUAKE/W1-D and QUAKE/W 1-D and QUAKE/W 2-D result 2-D in terms result of in acceleration terms of acceleration time history time and history spectral and accel-spec- traleration. acceleration. Figure 16 Figure shows 16 the shows surface the maximumsurface maximum acceleration acceleration along the along 2-D modelizationthe 2-D mod- elizationthrough thethrough QUAKE/W the QUAKE/W code. code.

FigureFigure 16. 16. SurfaceSurface acceleration acceleration profileprofile along along the the 2-D 2-D section section analyzed analyz throughed through QUAKE/W QUAKE/W code code for the for Amoruso the Amoruso et al. [26 et] input.al. [26] input.

Figures 17–19 show the 1-D and 2-D analysis for the Amoruso et al. [26] input, and the results have been summarized in Table 7. Appl. Sci. 2021, 11, 3180 15 of 23

Appl.Appl. Sci.Sci. 20212021,, 1111,, xx FORFOR PEERPEER REVIEWREVIEW 1616 ofof 2424 Figures 17–19 show the 1-D and 2-D analysis for the Amoruso et al. [26] input, and the results have been summarized in Table7.

FigureFigureFigure 17.17. ComparisonComparison betweenbetween 1-D1-D 1-D andand and 2-D2-D 2-D analysanalys analyseseses performedperformed performed byby by EERAEERA EERA andand and QUAKE/WQUAKE/W QUAKE/W forfor for point pointpoint 11 inin termsterms ofof accelerationacceleration timetime historyhistory andand spectralspectral acceleration,acceleration, forfor thethe AmorusoAmoruso etet al.al. [26][26] 1 in terms of acceleration time history and spectral acceleration, for the Amoruso et al. [26] input. input.input.

FigureFigureFigure 18.18. ComparisonComparison betweenbetween 1-D1-D 1-D andand and 2-D2-D 2-D analysanalys analyseseses performedperformed performed byby by EERAEERA EERA andand and QUAKE/WQUAKE/W QUAKE/W forfor for point point 2 in terms of acceleration time history and spectral acceleration, for the Amoruso et al. [26] 2point in terms 2 in terms of acceleration of acceleration time historytime history and spectraland spectral acceleration, acceleration, for for the the Amoruso Amoruso et al.et al. [26 [26]] input. input.input. Appl. Sci. 2021, 11, 3180 16 of 23 Appl. Sci. 2021, 11, x FOR PEER REVIEW 17 of 24

FigureFigure 19.19. ComparisonComparison betweenbetween 1-D 1-D and and 2-D 2-D analyses analyses performed performed by by EERA EERA and and QUAKE/W QUAKE/W for for point 3point in terms 3 in ofterms acceleration of acceleration time history time history and spectral and spectral acceleration, acceleration, for the for Amoruso the Amoruso et al. [26 et] al. input. [26] input. Table 7. PGA by 1-D and 2-D analyses for the Amoruso et al. [26] input at point 1, 2 and 3. Table 7. PGA by 1-D and 2-D analyses for the Amoruso et al. [26] input at point 1, 2 and 3.

PGAEERA PGAQUAKE/W 1-D PGAQUAKE/W 2-D PGAEERA PGAQUAKE/W 1-D PGAQUAKE/W 2-D [g] [g] [g] [g] [g] [g] Point 1 0.208 0.156 0.242 Point 1 0.208 0.156 0.242 Point 2 0.208 0.156 0.400 Point 32 0.1840.208 0.1520.156 0.138 0.400 Point 3 0.184 0.152 0.138 Table8 shows, for the same points, the result of 1-D and 2-D analysis carried out by Table 8 shows, for the same points, the result of 1-D and 2-D analysis carried out by the seismograms for the Tortorici et al. [25], Bottari et al. [24], DISS Messina Strait, DISS the seismograms for the Tortorici et al. [25], Bottari et al. [24], DISS Messina Strait, DISS Gioia Tauro, DISS Aspromonte Est, and 1693 Catania earthquakes. Gioia Tauro, DISS Aspromonte Est, and 1693 Catania earthquakes. Table 8. PGA by 1-D and 2-D analyses for the Tortorici et al. [25], Bottari et al. [24], DISS Messina Strait, DISS Gioia Tauro, DISSTable Aspromonte 8. PGA by 1-D Est, and 1693 2-D Catania analyses earthquake for the Tortorici inputs at et pointal. [25], 1, 2Bo andttari 3. et al. [24], DISS Messina Strait, DISS Gioia Tauro, DISS Aspromonte Est, 1693 Catania earthquake inputs at point 1, 2 and 3. Tortorici et al. [25] Bottari et al. [24] DISS Messina Strait Tortorici et al. [25] Bottari et al. [24] DISS Messina Strait PGAPGA PGAPGA PGAPGA PGAPGA PGAPGA PGAPGA PGAPGA PGAPGA PGAPGA EERA QUAKE/W 1-D QUAKE/W 2-D EERA QUAKE/W 1-D QUAKE/W 2-D EERA QUAKE/W 1-D QUAKE/W 2-D [g]EERA [g]QUAKE/W 1-D QUAKE/W [g] 2-D [g]EERA QUAKE/W [g] 1-D QUAKE/W [g] 2-D EERA [g] QUAKE/W [g] 1-D QUAKE/W [g] 2-D [g] [g] [g] [g] [g] [g] [g] [g] [g] Point 1 0.208 0.193 0.311 0.228 0.207 0.336 0.195 0.269 0.403 PointPoint 2 1 0.2080.208 0.1930.193 0.4000.311 0.2280.228 0.2070.207 0.3700.336 0.1950.195 0.2690.269 0.4930.403 PointPoint 3 2 0.1760.208 0.1470.193 0.0830.400 0.1680.228 0.1410.207 0.0640.370 0.1650.195 0.1510.269 0.1400.493 Point 3 0.176DISS Gioia Tauro0.147 0.083 0.168 DISS Aspromonte0.141 Est0.064 0.165 1693 Catania0.151 Earthquake 0.140 PGADISS GioiaPGA Tauro PGA PGA DISSPGA Aspromonte EstPGA PGA 1693 CataniaPGA EarthquakePGA EERAPGAQUAKE/W PGA 1-D QUAKE/WPGA 2-D EERAPGA QUAKE/WPGA 1-D QUAKE/WPGA 2-D EERAPGA QUAKE/WPGA 1-D QUAKE/WPGA 2-D [g]EERA [g]QUAKE/W 1-D QUAKE/W [g] 2-D [g]EERA QUAKE/W [g] 1-D QUAKE/W [g] 2-D EERA [g] QUAKE/W [g] 1-D QUAKE/W [g] 2-D Point 1 0.257[g] 0.203[g] 0.369[g] 0.206[g] 0.266[g] 0.493[g] 0.179[g] 0.142[g] 0.121[g] PointPoint 2 1 0.2570.257 0.2030.203 0.3730.369 0.2060.206 0.2660.266 0.5360.493 0.1790.179 0.1420.142 0.1400.121 Point 3 0.202 0.157 0.197 0.181 0.167 0.156 0.154 0.117 0.054 Appl. Sci. 2021, 11, x FOR PEER REVIEW 18 of 24

Point 2 0.257 0.203 0.373 0.206 0.266 0.536 0.179 0.142 0.140 Point 3 0.202 0.157 0.197 0.181 0.167 0.156 0.154 0.117 0.054

3.5. Topographic Effects It is well known that the topography affects the responses at the free surface by com- plicated cycles of amplification and de-amplification. In general, the responses are ampli- fied at the upper surface of slopes and attenuated at their base. Among the most important study of topographic amplification, we recall the experi- ence of Ashford and Sitar [45,46] and Ashford et al. [47], related to the seismic response of steep natural slopes. In this study, the site response was characterized by maximum acceleration at various locations as follows (Figure 20):

- afft, the maximum free field acceleration in front of the toe; - affc, the maximum free field acceleration behind the crest see Equation (4); - amax, the maximum crest acceleration. In this study, the topographic and site amplification were treated separately in order to determine the contribution of the different factors; therefore, three measures of ampli- fications were computed: At—Equation (3)—“topographic amplification,” the amplifica- tion of the free field motion at the crest; As—Equation (4)—“site amplification,” the am- plification due to the natural frequencies of the site; Aa—Equations (5) and (6)—“apparent amplification,” the apparent amplification of the motion between the base and the crest. The proposed parameters were obtained as follows: Appl. Sci. 2021, 11, 3180 17 of 23 a −a = max ffc At (3) a ffc 3.5. Topographic Effects It is well known that the topographya affects−a the responses at the free surface by complicated cycles of amplification and de-amplification.= ffc fft In general, the responses are As (4) amplified at the upper surface of slopes and attenuated at their base. afft Among the most important study of topographic amplification, we recall the experi- ence of Ashford and Sitar [45,46] and Ashford et al. [47], related to the seismic response a − a of steep natural slopes. In this study, the= sitemax responsefft was characterized by maximum acceleration at various locations as followsAa (Figure 20): (5) afft - afft, the maximum free field acceleration in front of the toe;

- affc, the maximum free field acceleration behind the crest see Equation (4); - amax, the maximum crest acceleration.Aa = (1 + At)(1 + As) − 1 (6)

FigureFigure 20. 20. AshfordAshford and and Sitar’s Sitar’s [46] [46] model model for for the the topographical topographical amplification amplification evaluation. evaluation.

In this study, the topographic and site amplification were treated separately in order to determine the contribution of the different factors; therefore, three measures of amplifi- cations were computed: At—Equation (3)—“topographic amplification,” the amplification of the free field motion at the crest; As—Equation (4)—“site amplification,” the amplifi- cation due to the natural frequencies of the site; Aa—Equations (5) and (6)—“apparent amplification,” the apparent amplification of the motion between the base and the crest. The proposed parameters were obtained as follows:

amax − a f f c At = (3) a f f c

a f f c − a f f t As = (4) a f f t

amax − a f f t Aa = (5) a f f t

Aa = (1 + At)(1 + As) − 1 (6) The results of numerical analyses carried out for the input (Bottari et al. [24]; Tortorici et al. [25]; Amoruso et al. [26]; DISS Aspromonte Est; DISS Gioia Tauro; DISS Messina Strait), and based on the Ashford approach, are shown in the Table9. Appl. Sci. 2021, 11, x FOR PEER REVIEW 19 of 24

The results of numerical analyses carried out for the input (Bottari et al., [24]; Tor- torici et al., [25]; Amoruso et al., [26]; DISS Aspromonte Est; DISS Gioia Tauro; DISS Mes- sina Strait), and based on the Ashford approach, are shown in the Table 9. Results show a topographical amplification coefficient, given by 1+At greater than 1.20, while the same coefficient given by NTC 2018 for the study area is equal to 1.20.

Table 9. Different results for the Ashford et al. [47] model.

Input At As Aa Bottari et al. [24] 0.10 4.29 4.81 Tortorici et al. [25] 0.29 2.76 3.83 Amoruso et al. [26] 0.65 0.76 1.91 DISS Messina Strait 0.22 1.88 2.52 Appl. Sci. 2021, 11, 3180 18 of 23 DISS Gioia Tauro 0.01 0.87 0.89 DISS Aspromonte Est 0.09 2.16 2.43 1693 Catania Earth- 0.16 1.24 1.59 Table 9. quakeDifferent results for the Ashford et al. [47] model.

Input At As Aa Topographic amplification can be also measured by the ratio between the Fourier spectrumBottari of the et seismogram al. [24] at the crest 0.10 (10 m away) and the 4.29 Fourier spectrum 4.81 of the free Tortorici et al. [25] 0.29 2.76 3.83 field seismogramAmoruso et al.behind [26] the crest (250 0.65 m away). This is the 0.76 so-called TAF (Topographic 1.91 AggravationDISS Messina Factor) Strait which is defined in 0.22 the frequency domain, 1.88 after Kallou et 2.52al. [48]. FigureDISS 21 Gioia shows Tauro the Topographic 0.01 Aggravation Factor 0.87(TAF), after the Kallou 0.89 et al. [48] approach,DISS Aspromonte for the EstAmoruso et al. [26] 0.09 input. Results show 2.16 values of TAF reaching 2.43 on average1693 Cataniaabout 1.45 Earthquake in the frequency range 0.16 f of 1–5 Hz. 1.24 1.59 The topographic amplification can be also evaluated in the time domain following

the approachResults showproposed a topographical by Bouckovalas amplification and Kouretzis coefficient, [49] in terms given of by the 1 + (2-D)/(l-D)At greater ratio than of1.20, elastic while response the same spectra coefficient obtained given at bythe NTC crest. 2018 Figure for 22 the shows study the area Topographic is equal to 1.20. Aggra- vationTopographic Factor (TAF) amplification after the Bouckovalas can be also and measured Kouretzis by [49] the approach ratio between for the the Amoruso Fourier etspectrum al. [26] input. of the In seismogram this case, results at the crestshow (10 high m away)values andof TAF, the Fourierreaching spectrum on average of the about free 1.42field for seismogram the period behindrange T the of crest0.20 to (250 1.0 m s.away). Obtained This values is the are so-called in agreement TAF (Topographic with large amplificationsAggravation Factor) obtained which for similar is defined studies in the performed frequency on domain, ridges, after slopes Kallou and valleys. et al. [48 ]. FiguresFigure 21 23 shows and 24 the show, Topographic respectively, Aggravation the comparison Factor (TAF), between after theFourier Kallou amplitude et al. [48] spectraapproach, at the for crest the (1-D Amoruso and 2-D) et al. and [26 behind] input. the Results crest (2-D) show and values between of TAF elastic reaching response on spectraaverage at about the crest 1.45 (1-D in the and frequency 2-D) and range behind f of the 1–5 crest Hz. (2-D).

FigureFigure 21. 21. TopographicTopographic Aggravation Aggravation Factor Factor (TAF), (TAF), after after the the Kallou Kallou et et al. al. [48] [48] approach, approach, obtained obtained as asthe the ratio ratio of theof the Fourier Fourier amplitude amplitude spectra spectra at the at crest the and crest behind and behind the crest, the for crest, the Amoruso for the Amoruso et al. [26] inputet . al. [26] input. The topographic amplification can be also evaluated in the time domain following the approach proposed by Bouckovalas and Kouretzis [49] in terms of the (2-D)/(l-D) ratio of elastic response spectra obtained at the crest. Figure 22 shows the Topographic Aggravation Factor (TAF) after the Bouckovalas and Kouretzis [49] approach for the Amoruso et al. [26] input. In this case, results show high values of TAF, reaching on average about 1.42 for the period range T of 0.20 to 1.0 s. Obtained values are in agreement with large amplifications obtained for similar studies performed on ridges, slopes and valleys. Appl. Sci. 2021, 11, x FOR PEER REVIEW 20 of 24 Appl. Sci. 2021, 11, 3180 19 of 23

Appl. Sci. 2021, 11, x FOR PEER REVIEW 20 of 24

FigureFigure 22. 22. TopographicTopographic Aggravation Aggravation Factor (TAF), afterafter thethe Bouckovalas Bouckovalas and and Kouretzis Kouretzis [49 [49]] approach, ap- proach,in terms in of terms (2-D)/(l-D) of (2-D)/(l-D) ratio of elastic ratio response of elastic spectra response obtained spectra at the obtained crest, for at the theAmoruso crest, for et the al. [26] input.

Amoruso et al. [26] input. FigureFigures 22. Topographic 23 and Aggravation24 show, respectively, Factor (TAF), the after comparison the Bouckovalas between and Kouretzis Fourier amplitude[49] ap- proach,spectra in at terms the crestof (2-D)/(l-D) (1-D and ratio 2-D) of andelastic behind response the spectra crest (2-D) obtained and at between the crest, elastic for the response Amorusospectra atet theal. [26] crest input. (1-D and 2-D) and behind the crest (2-D).

Figure 23. Comparison between Fourier amplitude spectra at the crest (1-D and 2-D) and behind the crest (2-D), for the Amoruso et al. [26] input.

FigureFigure 23. 23. ComparisonComparison between between Fourier Fourier amplitude amplitude spectr spectraa at the crest (1-D and 2-D) andand behindbehind the thecrest crest (2-D), (2-D), for for the the Amoruso Amoruso et al.et al. [26 [26]] input. input. Appl. Sci. 2021, 11, x FOR PEER REVIEW 21 of 24 Appl. Sci. 2021, 11, 3180 20 of 23

FigureFigure 24. 24. ComparisonComparison between between elastic elastic response response spectra spectra at atthe the crest crest (1-D (1-D and and 2-D) 2-D) and and behind behind the the crestcrest (2-D), (2-D), for for the the Amoruso Amoruso et et al. al. [26] [26 ]input. input.

4.4. Discussion Discussion and and Conclusions Conclusions The study of the response of a subjected to seismic actions is often conducted The study of the response of a subsoil subjected to seismic actions is often conducted for different purposes. It allows the prediction of permanent soil deformations and the for different purposes. It allows the prediction of permanent soil deformations and the quantification of the risk of instability phenomena, such as landslides or liquefaction triggering. quantification of the risk of instability phenomena, such as landslides or liquefaction trig- In this paper, a study on the evaluation of the topographic effects for a slope in the gering. Tyrrhenian area of has been carried out. Detailed geotechnical characteriza- In this paper, a study on the evaluation of the topographic effects for a slope in the tion was also carried out by in situ and laboratory tests. The laboratory tests performed Tyrrhenian area of Southern Italy has been carried out. Detailed geotechnical characteri- in the static field made it possible to evaluate the mechanical characteristics of the soil, zation was also carried out by in situ and laboratory tests. The laboratory tests performed allowing to obtain the fundamental parameters as a function of depth such as unit weight, in the static field made it possible to evaluate the mechanical characteristics of the soil, moisture content, Atterberg limits, void ratio, porosity and degree of saturation; moreover, allowing to obtain the fundamental parameters as a function of depth such as unit weight, through direct shear tests it was possible to obtain the values of the cohesion and the moisture content, Atterberg limits, void ratio, porosity and degree of saturation; moreo- angle of shear resistance. The laboratory tests performed in the dynamic field allowed ver,for through evaluating direct the non-linearshear tests behaviorit was possible of soils to in obtain terms the of stiffnessvalues of attenuation the cohesion with and strain the angle of shear resistance. The laboratory tests performed in the dynamic field allowed for G/Go-γ and the damping ratio evolution with strain D-γ. Moreover, the results obtained evaluatingthrough the the Down non-linear Hole (DH)behavi testsor of made soils it in possible terms toof derivestiffness the attenuation trend with thewith depth strain of G/Gtheo shear-γ and wave the damping velocityand ratio other evolution parameters with strain such as D- theγ. Moreover, Poisson ratio the and results the coefficientobtained throughof earth the pressure Down at Hole rest. (DH) tests made it possible to derive the trend with the depth of the shearThe wave definition velocity of seismicand other action parameters was based such on as synthetic the Poisson seismograms ratio and the related coefficient to the of1908 earth Messina pressure and at Reggiorest. Calabria earthquake and the 1693 Val di Noto earthquake. TheA numerical definition model of seismic based action on the was 1-D EERAbased andon synthetic 2-D QUAKE/W seismograms codes wasrelated performed to the 1908for theMessina slope and model Reggio in the Calabria Caronia earthquake area, subjected and tothe vertically 1693 Val propagating di Noto earthquake. in-plane shear wavesA numerical (Vs waves). model Results based show on the that 1-D stratigraphic EERA and 2-D amplification QUAKE/W and codes topographic was performed ampli- forfication the slope effects model were in foundthe Caronia to interact, area, subjec suggestingted to thatvertically to accurately propagating predict in-plane topographic shear waveseffects (V thes waves). two effects Results should show not that be stratigraphic always handled amplification separately. and topographic amplifi- cation1-D effects computer were found codes to have interact, been usedsuggesting to model that the to equivalent-linear accurately predict earthquake topographic site effectsresponse the two analyses effects of should layered not slope be always deposits, handled as generally separately. performed by professionals. Because1-D computer the slope codes is moderate have been (average used slopeto mo angledel the is equivalent-linear i = 22◦), a 1-D response earthquake analysis, site responseoften used analyses by professionals, of layered slope was the deposits, first step as ofgenerally the study, performed as indicated by professionals. by the provisions Be- causeof national the slope and is international moderate (average building slope codes. angl Besides,e is i = 22°), the locala 1-D seismic response response analysis, analysis often usedhas beenby professionals, also performed was in the greater first detail step of using the astudy, counted as 2-Dindicated simple by model. the provisions Results show of nationalamplification and international of the seismic building motion codes. using initiallyBesides, the the 1-D local code. seismic Besides, response by performing analysis has the been2-D analysis,also performed further in amplification greater detail of theusin seismicg a counted acceleration 2-D simple at the model. crest of Results the slope show was amplificationfound. By the of numerical the seismic analyses, motion threeusing points initially in thethe slope1-D code. cross-section Besides, wereby performing monitored theas 2-D follows: analysis, point further 1 located amplification behind the of crestthe seismic of the slope;acceleration point at 2 locatedthe crest at of the the crest slope of Appl. Sci. 2021, 11, 3180 21 of 23

the slope; point 3 downstream sufficiently far from the foot of the slope. This result is in agreement with the Ashford and Sitar [46] approach, as shown in Table8, where the values of the topographic amplification are presented. An average value of the topographic amplification At = 0.22 was observed, with a maximum value of At = 0.65 using as an input motion the Amoruso et al. [26] seismograms related to the Messina and Reggio Calabria 1908 earthquake. Comparing 1-D with 2-D results, the stratigraphic site amplification and the Topo- graphic Aggravation Factor (TAF) were also computed. The evaluation of the Topographic Aggravation Factor (TAF), after the Kallou et al. [48] approach, shows values of TAF reaching on average about 1.45 in the frequency range f of 1–5 Hz. The evaluation of the Topographic Aggravation Factor (TAF) following the approach proposed by Bouckovalas and Kouretzis [49]) shows values of TAF reaching on average about 1.42 for the period range T of 0.20 to 1.0 s. Concerning the Italian Technical Building Code [10], it should be emphasized that the Code identifies four different topographic categories, each of which is associated with a value of the topographic amplification factor St, with a maximum value of St = 1.40 in the case of slopes with an inclination greater than 30◦. In the case of a slope inclination less than 30◦, as in the Caronia area, the NTC 2018 provides a maximum value of the topographic amplification factor St = 1.20. Therefore, the provisions of the Code NTC 2018 predict rather moderate effects compared to those predicted by the 2-D analyses. The aim of the study is that it will form a basis for the design of works in the Caronia area and can provide a basis for professional works.

Author Contributions: A.C., A.F., S.G. and A.P. contributed equally to design the research, process the corresponding data, draft, organize and finalize the paper. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. Data Availability Statement: All data and codes performed during the study appear in the paper. Conflicts of Interest: The authors declare no conflict of interest.

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