VOLCANIC SOIL CHARACTERISATION AND SITE RESPONSE ANALYSIS IN THE CITY OF CATANIA ABSTRACT

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1 VOLCANIC SOIL CHARACTERISATION AND SITE RESPONSE ANALYSIS IN THE CITY OF CATANIA A. Cavallaro 1, S. Grasso 2 and M. Maugeri 3 ABSTRACT According to the frequency and the importance of the seismic effects suffered in past times, the city of Catania, located on the eastern zone of Sicily, must be considered one of the most high risk seismic areas in Italy. This paper describes and compares the results of in situ and laboratory investigations that were carried out in order to determine the soil dynamic characteristics in the test site of "Via Monterosso" in the city of Catania. The site mainly consists of an alternance of lava in blocks, scoriaceous lava, grey-black pyroclastic sand and red volcanic rocks. The following in situ investigations were carried out in order to determine the soil profile and the geotechnical characteristics for the volcanic soil and rock site under consideration, with special attention for the variation of shear modulus and damping with depth: Down Hole (D-H) tests and geotechnical borings. Moreover, the following laboratory investigations were carried out on undisturbed samples retrieved with a 86 mm diameter Shelby sampler: Resonant Column and Torsional shear tests; Oedometer tests; Direct shear tests. The laboratory results for G and D were compared with those obtained for similar soil types. It was also possible to compare in situ and laboratory small shear modulus and to determine the G-γ curve for soil non-linearity evaluation. Moreover, two expressions were proposed respectively to allow the complete shear modulus degradation with strain level and the inverse variation of damping ratio with normalized shear modulus. Finally, synthetic seismograms have been drawn for the site long a set of six receivers placed at different depths, starting from the surface up to almost 170 m. After evaluating the synthetic accelerograms at the bedrock, the ground response analysis at the surface, in terms of time histories and response spectra, has been obtained by a 1-D non-linear model. Introduction It is well known that local geological and topographic conditions play a major role on 1 Researcher, Ph. Doctor in Geotechnical Engineering, CNR-IBAM, Viale Andrea Doria n. 6, Catania, Italy 2 Ph. Doctor in Geotechnical Engineering, University of Catania, Department of Civil and Environmental Engineering, Viale Andrea Doria n. 6, Catania, Italy 3 Full Professor in Geotechnical Engineering, University of Catania, Department of Civil and Environmental Engineering, Viale Andrea Doria n. 6, Catania, Italy

2 earthquake ground motions and distribution of damage. This aspect becomes even more critical in areas with sharp transitions between stiff surface formations and softer soil materials, typically found in a volcanic zone like Catania, which lies at the foot of the Mt. Etna volcano and was affected by many eruptions in historical and pre-historic times. Hence, a substantial effort was devoted to the zonation and seismic characterization of soils in the Catania area. This task was carried out both by exploiting the existing data and by performing special investigations at some selected sites. Laboratory cyclic tests were performed to characterize the non linear soil behaviour, which may occur during strong earthquakes, such as the 1693 and the 1818 scenario earthquakes. This paper describes and compares the results of in situ and laboratory investigations that have been carried out in order to determine the soil dynamic characteristics in the test site of "Via Monterosso", located in the northern center of the city of Catania, where the effusive materials from the Etna volcano predominate. On this site is located a four-stories tall reinforced concrete building, built at the end of 70s and heavy damaged by the South Eastern Sicily earthquake of December 13, 1990 (M L = 5.8). A borehole was made in the test site of "Via Monterosso" (Fig. 1), in which down-hole velocity measurements have been executed, and undisturbed samples were retrieved. Resonant Column Tests (RCT) and Cyclic Loading Torsional Shear Tests (CLTST) were performed to investigate the initial shear modulus G o and shear modulus degradation with shear strain, as well as damping ratio degradation. Investigation Program Many stratigraphic boreholes have been considered in the framework of The Catania Project (Pastore and Turello 2000), in the area where is located the building. The site mainly consists of an alternance of lava in blocks, scoriaceous lava, grey-black pyroclastic sand and red volcanic rocks. The following in situ investigations were carried out in order to determine the detailed soil profile and the geotechnical characteristics for the volcanic soil under consideration, with special attention for the variation of shear modulus and damping with depth: Down Hole (D-H) tests and geotechnical borings. Moreover, the following laboratory investigations were carried out on undisturbed samples retrieved with a 86 mm diameter Shelby sampler: Resonant Column and Torsional shear tests; Oedometer tests; Direct shear tests. The laboratory results for G and D were compared with those obtained for similar soil types. It was also possible to compare in situ and laboratory small shear modulus and to determine the G-γ curve for soil non-linearity evaluation. Shear Modulus and Damping Ratio Shear modulus G and damping ratio D of Catania deposits were obtained in the laboratory by Resonant Column/Torsional shear apparatus (Lo Presti et al. 1993). G is the unload-reload shear modulus evaluated from RCT, while G o is the maximum value or also "plateau" value as observed in the G-log(γ) plot. Generally G is constant until a e certain strain limit is exceeded. This limit is called elastic threshold shear strain ( γ t ) and it is believed that soils behave elastically at strains smaller than γ e t. The elastic stiffness at γ < γ e t is thus the already defined G o.

3 Top soil and fill Fractured to slightly fractured lavas Scoriaceous lavas Volcanoclastic rocks Scoriaceous lavas Fractured to slightly fractured lavas Scoriaceous lavas Volcanoclastic rocks Fractured to slightly fractured lavas Pyroclastic rocks and red volcanoclastic rocks Figure 1. "Via Monterosso" borehole profile with down-hole velocity measurements. For resonant column tests (RCTs) the damping ratio was determined, during the resonance condition, using the steady-state method. Moreover, the laboratory test results at small strain were compared with in situ seismic tests and in particular with a Down Hole test (D-H). Shear Modulus and Damping Ratio from Laboratory Tests Fig. 2 shows the results of RCTs normalised by dividing the shear modulus G(γ) for the initial value G o at very low strain. The experimental results of volcanic soil specimens were used to determine the empirical parameters of the eq. proposed by Yokota et al. (1981) to describe the shear modulus decay with shear strain level: G(γ) 1 = β G o 1+ αγ(%) (1) in which: G(γ) = strain dependent shear modulus; γ = shear strain (in percent); α, β = soil constants. The expression (1) allows the complete shear modulus degradation to be considered with strain level. The values of α = 7.5 and β = were obtained for a volcanic soil. Moreover (Fig. 2b) the degradation of the shear modulus with shear strain level have been compared with the behaviour based on plasticity index (I P ), proposed by Vucetic and Dobry (1991). In Fig. 3a the damping ratio values obtained from RCT are shown.

4 As suggested by Yokota et al. (1981), the inverse variation of damping ratio with respect to the normalised shear modulus (Fig. 3b) has an exponential form given by the following equation: G( γ) D( γ)(%) = η exp λ (2) G o in which: D(γ) = strain dependent damping ratio; γ = shear strain; η, λ = soil constants. The values of η = 90 and λ = 4.5 were obtained for a volcanic soil. This relation in any case will not work as strain exceed about 1 %. The same expression was used by Carrubba and Maugeri (1988), Cavallaro et al. (1999); Cavallaro et al. (2001), Cavallaro et al. (2005) and Cavallaro and Maugeri (2005), to evaluate the empirical parameters for different soil types in different test sites (Table 1). Moreover (Fig. 3c) the increasing of damping with shear strain level have been compared with the behaviour based on plasticity index (I P ), proposed by Vucetic and Dobry (1991). Shear Modulus from in Situ Tests Dynamic in situ tests were performed in Via Monterosso area. In Figure 4a the Poisson ratio variation with depth, obtained from a Down Hole (D-H) test, is plotted to show site characteristics. It is seen that the values oscillates around A comparison between G o values obtained from in situ test performed on the area under consideration with in situ tests performed in other volcanic soil test sites are shown in Fig.4b. The Down Hole test performed in St. Nicola alla Rena Church area showed G o values increasing with depth G/Go Test N. 1 Test N. 2 Test N. 3 Yokota et al. (1981) CATANIA - RCT Volcanic Soil γ [%] G/G o Vucetic & Dobry (1991) Cat ania Plain Clay Carrubba & Maugeri (1988) Cat ania Central Clay Cavallaro & Maugeri (1999) IP = 25% Via Stellata IP = 26% Cavallaro et al.(1999) Piazza Palestro IP = 15% Cavallaro & Maugeri (2005) San Nicola alla Rena Churc Cavallaro et al.(2001) Via Dottor Consoli Cavallaro et al.(2005) IP = 31% =15% IP = 24% IP = 0-15% =0% =200% =100% =50% =30% γ (%) (a) (b) Figure 2. a) G/G o -γ curves from RCTs for Monterosso volcanic soil; b) Comparison between the degradation of the shear modulus with shear strain level for Catania clay and plasticity index.

5 D [%] Test N. 1 Test N. 2 Test N. 3 CATANIA - RCT Volcanic Soil D [%] Test N. 1 Test N. 2 Test N. 3 Yokota et al. (1981) 5 CATANIA - RCT Volcanic Soil γ [%] (a) D (%) Vucetic & Dobry (1991) Catania Plain Clay I P = 31% Carrubba & Maugeri (1988) Catania Central Clay IP = 25% Cavallaro & Maugeri (1999) Via Stellata I P = 26% Cavallaro et al.(1999) Piazza Palestro IP = 15% Cavallaro & Maugeri (2005) San Nicola alla Rena Churc Cavallaro et al.(2001) IP = 0-15% Via Dottor Consoli Cavallaro et al.(2005) I P = 24% G/G o =0% =15% =30% =50% =100% =200% (b) γ (%) (c) Figure 3. a) D-γ curves from RCTs for Monterosso volcanic soil; b) D-G/G o curves from RCTs for Monterosso volcanic soil; c) Comparison between the increasing of damping with shear strain level for Catania clay and plasticity index. Table 1. Soil constants for Catania areas. Site α β η λ 1. Piana di Catania Plaja beach Via Stellata Piazza Palestro San Nicola alla Rena Church Via Monterosso 8. Via Dottor Consoli In the same Figure, G o values obtained from D-H test performed in Tavoliere area and in St. Nicola alla Rena Church area are also showed (Cavallaro et al. 2001). In Tavoliere area, located in the N-W zone of the city of Catania, deposits mainly present lava and tuff strata interbedded with soils lenses of variable thickness mainly consisting of sand and gravel (GC from 20 to 50 %) in the first 10 m. In the St. Nicola alla Rena Church area (Cavallaro et al. 2001) the lava and tuff strata are interbedded with soils lenses of variable thickness mainly consisting of sand and gravel (GC from 15 to 26 %).

6 0 4 Poisson ratio V s [m/s] CATANIA DOWN - HOLE H [m] CATANIA"Via Monterosso" DOWN-HOLE H [m] Via M onterosso San Nicola alla Rena Tavoliere (a) (b) Figure 4. a) Poisson ratio from in situ tests; b) Shear wave velocity from in situ tests. The natural moisture contents ranged from 21 to 30 % and the specific gravity values G s ranged from 2.88 to The lava blocks, retrieved for a depth ranged between 9.2 to 29.3 m, were subjected to unconfined axial compression, and the obtained strength results assumed a minimum value of MPa and a maximum value of MPa. The RQD (Rock Quality Designation) values obtained for the lava blocks ranged between 40 and 100 %. For Tavoliere site, very high values of G o (i.e., not less than 400 MPa for depths greater than 5 m) can be assumed. In Saint Nicola alla Rena Church area very high values of G o are obtained. According to these data for Via Monterosso area, it is possible to assume G o equal to about 200 MPa for depths of about 15 m. 1-D Non-Linear Analysis of the Ground Motion at the Surface The scenario earthquake has been evaluated by synthetic accelerograms. The approach adopted is based on the modeling of the source mechanism in a 2-D section, by the 2-D fullwave seismic equation through the Chebyshev Spectral Element Method (SPEM) (Priolo 2000). Synthetic seismograms have been drawn for the Via Monterosso test site long a set of six receivers placed at different depths, starting from the surface up to almost 170 m. Synthetic seismograms are computed up to a maximum frequency of 8 Hz and for a total propagation time of 20s. To evaluate the seismic response at the surface, the synthetic accelerogram evaluated at 21 m depth, was used as input motion at the base of the 1-D column of 20 m height. Also scaled recorded accelerograms of the South Eastern Sicily earthquake of December 13, 1990 have been used. The evaluation of local site effects due to a column of 20m was made by 1-D non-linear code. The code implements a one-dimensional simplified, hysteretic model for the non-linear soil response (Frenna and Maugeri 1995). The column is subdivided in several, horizontal, homogeneous and isotropic layers characterized by a non-liner spring stiffness G(γ), a dashpot damping D(γ) and a soil mass density ρ. Moreover, to take into account the soil non-linearity, laws of shear modulus, given by Equation (1), and material damping ratio against strain, given by Equation (2) have been inserted in the code. The 1-D column has a height of 20 m and is excited at the base by the scenario earthquake. Seismic response at the soil surface The soil response in the free field and also considering the surcharge at the top of the soil

7 profile, is evaluated for the soil profile given by soil stratigraphy reported in Fig. 1. The analysis provides the time-history response in terms of displacements, velocity and acceleration at the surface. Using this time history, response spectra concerning the investigated site can be deduced. The structure surcharge was fixed in 65 kn/m 2, depending on the loading analysis performed for the reinforced concrete building. Globally 24 elastic response spectra and 24 inelastic design spectra have been plotted. A comparison has been also performed between elastic and inelastic spectra derived varying G o values obtained from in situ tests performed on the area under consideration and from laboratory tests; results of this comparison are shown in Fig.5. In each graphic it is possible to observe different spectra in free field (5a), (5b) and (5c) and also considering the structural surcharge (5d), (5e) and (5f), for the input synthetic accelerogram related to the 1693 scenario earthquake (5a) and (5d) and for the scaled recorded accelerograms of the South Eastern Sicily earthquake of December 13, 1990 (5b), (5c), (5e) and 2,800 5,500 1,500 2,400 Monterosso (DH da S.Nicola) Monterosso (DH da Monterosso) Monterosso (prove laboratorio S.Nicola) 5,000 4,500 Monterosso (DH da S.Nicola) Monterosso (DH da Monterosso) Monterosso (prove laboratorio S.Nicola) Monterosso (DH da S.Nicola) Monterosso (DH da Monterosso) Monterosso (prove laboratorio S.Nicola) 2,000 Monterosso (Vs da Jamilolkowsky) 4,000 Monterosso (Vs da Jamilolkowsky) Monterosso (Vs da Jamilolkowsky) 1,600 3,500 3,000 0,900 2,500 2,000 0,600 0,800 1,500 0,300 0,400 0,500 (a) (b) (c) 2,500 4,500 2,500 2,000 Monterosso (DH S.Nicola) Monterosso (DH Monterosso) Monterosso (prove laboratorio da S.Nicola) 4,000 3,500 Monterosso (DH S.Nicola) Monterosso (DH Monterosso) Monterosso (prove laboratorio da S.Nicola) 2,000 Monterosso (DH S.Nicola) Monterosso (DH Monterosso) Monterosso (prove laboratorio da S.Nicola) Monterosso (Vs da Jamiolkowsky) 3,000 Monterosso (Vs da Jamiolkowsky) Monterosso (Vs da Jamiolkowsky) 1,500 2,500 1,500 2,000 1,500 0,500 0,500 0,500 (d) (e) (f) Figure 5. Comparisons between the elastic response spectra at the surface obtained varying Go. (5f). The soil spectra have been evaluated for different G o values, obtained from D-H test performed in Via Monterosso area and in St. Nicola alla Rena Church area and from different laboratory tests, such as RCT tests performed on undisturbed samples retrieved in Via Monterosso area and void ratio evaluation by means of empirical correlation with G o given by Jamiolkowski et. al. (1995). The elastic response spectra have been also subdivided in different groups to investigate the effects of the structural surcharge presence. These spectra have been compared with those suggested by the European Code No. 8 (CEN 2003) and by the new Italian O.P.C.M (O.P.C.M. 3274, 2003) for soil type C. Moreover, all the computed spectra refer also to a damping ratio ξo = 5 %. Then, the inelastic spectra are derived from the elastic response spectra including the structure ductility. The inelastic design spectra have been evaluated on the basis of the elastic response spectra utilizing the following expression: Sa Sd g = (3) g b where S a /g is the ordinate of the generic elastic response spectrum and S d /g is the ordinate of the corresponding inelastic spectrum and b is the normalized yield strength of the

8 structure if we consider that it behaves as an elasto-plastic structure, and so it is related to the structure ductility. In the present case the quantity b is evaluated according to Giuffrè and Giannini (1982), by means of the structure ductility µ, which is assumed equal to 2.5 for the Via Monterosso r.c. building. These last spectra have been also compared with those suggested by the European Code No. 8 (CEN 2003) and by the new Italian O.P.C.M (O.P.C.M ), in order to propose a site-dependent inelastic spectrum for "Via Monterosso" r.c. building. In the last case, the structure behavior factor q for the Via Monterosso r.c. building is fixed equal to 4.7, according to EC8. It has substantially the same meaning of the quantity b given by expression (3). Comparisons between obtained inelastic spectra with those proposed by the European code No. 8 and by the new Italian O.P.C.M. are reported in Fig. 6. The first graphic on the left (6a) refers to the inelastic spectra computed considering and neglecting the structural surcharge and for the input synthetic accelerogram related to the 1693 scenario earthquake; while the graphic on the right (6b) refers to the inelastic spectra computed considering and neglecting the structural surcharge computed for the Catania N-S component (a max = 2.43 m/s 2 ) of the input recorded accelerogram of the South Eastern Sicily earthquake of December 13, 1990; both of them have been compared with the spectra proposed by EC8 and O.P.C.M. Codes. Fig. 7 shows the inelastic spectra related respectively to the maximum peak of the spectral acceleration and to the minimum peak of the spectral acceleration. It is then possible to observe a quite significant gap between the maximum and minimum values of the peak spectral acceleration. It is possible also to observe some important divergences in terms of the critical periods, i.e. of the periods at which the maximum and minimum peaks of the spectral acceleration are reached. Then, a medium inelastic spectrum is evaluated, considering the average value of all the S d /g quantities present for a fixed period T. Then, globally, 4 medium inelastic spectra are obtained. These last spectra are reported in Fig. 7; finally, a global medium inelastic spectrum has been derived from the previous 4 medium inelastic spectra (Fig. 8). A Site-Dependent Inelastic Spectrum for Via Monterosso Test Site Comparing the 4 obtained medium inelastic spectra with the design spectra suggested by EC8 and by the new Italian O.P.C.M. a specific site-dependent inelastic spectrum is proposed for via Monterosso site, as shown in Fig. 8. Fig. 8 shows also a global medium inelastic spectrum deriving from the 4 medium inelastic spectra above mentioned. 1,400 PLASTIC mrosso2ff PLASTIC mrosso3ff PLASTIC mrosso4 FF PLASTIC mrosso2cs PLASTIC mrosso3cs 1,400 mrosso2ff mrosso3ff mrosso4 FF mrosso3cs mrosso4cs EC8 O.P.C.M. mrosso2cs PLASTI mrosso4cs PLASTIC EC8 PLASTIC O.P.C.M 0,800 0,800 0,600 0,600 0,400 0,400 0,200 0,200 (a) (b) Figure 6: Comparisons between the inelastic spectra given by synthetic accelerogram related to the 1693 earthquake (a) and by 1990 earthquake (b), at the soil surface with the design spectra suggested by EC8 and by the new Italian O.P.C.M.

9 0,400 B3R3RAD-FF 1,400 B3R3RAD-FF 0,350 0,300 B3R3RAD-CS CATAN_NS-FF CATAN_NS-CS SORT_EW-FF SORT_EW-CS SPETTRO MEDIO (Sp2) B3R3RAD-CS CATAN_NS-FF CATAN_NS-CS SORT_EW-FF SORT_EW-CS SPETTRO MEDIO (Sp3) 0,250 0,800 0,200 0,600 0,150 0,100 0,400 0,050 0,200 (a) (b) Figure 7. Medium inelastic spectra at the soil surface. a) Vs from D-H test performed in Via Monterosso area; b) Vs from RCT tests performed on retrieved undisturbed samples. As it is possible to see from Fig. 8 both the design spectra suggested by EC8 and by the new Italian O.P.C.M. do not cover the global medium computed inelastic spectrum, as well as, the 4 medium inelastic spectra, in the range of T equal to sec, which is generally the most critical period range for Catania structures. The period of the r.c. Monterosso building was 0.484s. Then, a new inelastic spectrum is proposed for via Monterosso site. In particular, the proposed inelastic spectrum, which can be considered a site-dependent inelastic spectrum, is obtained from the new Italian O.P.C.M. design spectrum for ground type C, adding the two new parameters S L and λ, as reported below: 0 T T T 2.5 B S = a S 1+ S 1 (4) d g L T T B T C T T C T D T T D S S S d d T B 2.5 a g S S L q q = (5) = a g S S L λ 2.5 TC q T 2.5 TCTD = ag S S L 2 q T λ (6) d (7) The new parameter S L represents the ratio between the average value of the 4 medium inelastic spectra and the maximum value of the design spectrum suggested by the new Italian O.P.C.M. in the range T B - T C. Thus, the ratio S L, equal in the present case to 2.15, represents the local soil parameter for the site condition underneath Monterosso building. The new parameter λ = 1.5 is introduced into expressions (6) and (7), which refers to the decreasing branch of the proposed inelastic spectrum, in order to achieve a decreasing of the proposed spectrum with the period increasing more rapid than that of the design spectra suggested by the new Italian O.P.C.M., as well as by EC8. Introducing λ the proposed site-dependent inelastic spectrum can fits the decreasing branch of the computed medium inelastic spectra better, being at the same time over the design spectra suggested by the new Italian O.P.C.M., and by EC8. Conclusions In this paper some information concerning G and D of Via Monterosso site in the Catania municipal area for seismic response analysis have been presented. Available data enabled one to define the small strain shear modulus profile to describe the G and D variation with strain level. Experimentally determined Go profiles from in situ tests were compared to that inferred from laboratory test results. It was then possible to evaluate the seismic response of the soil in the upper 20 m with a 1-D non-linear code. The excitation at the base of model are synthetic accelerograms, which refer to the 1693 scenario

10 1,400 EC8 O.P.C.M MEDIUM SPECTRUM DESIGN SPECTRUM 0,800 0,600 0,400 0,200 Figure 8. A new proposed site-dependent inelastic design spectrum compared with the design spectra suggested by EC8 and the new Italian O.P.C.M. earthquake (M= ), considering an extended source model, or scaled recorded accelerograms of the South Eastern Sicily earthquake of December 13, 1990 (ML=5.8). A new inelastic spectrum is proposed for the Monterosso building. In particular, the proposed inelastic spectrum, which can be considered a site-dependent design spectrum, is obtained from the new Italian O.P.C.M. design spectrum for ground type C, adding two new parameters SL and λ. The vulnerability analyses developed by others research groups on Via Monterosso reinforced concrete building, designed and built in the city of Catania without any seismic provision, confirm the high vulnerability of those structures. Particularly it can be stated that the analysed structures are not adequate to survive the seismic events which the seismic response at the surface defined: the expected PGA values are about in the range equal to 0.36 g, whereas the seismic strength of the building is able to resist up to 0.1 g. References Carrubba, P. and Maugeri, M. (1988). Determinazione delle Proprietà Dinamiche di un Argilla Mediante Prove di Colonna Risonante. Rivista Italiana di Geotecnica, Vol. 22, No. 2, pp Cavallaro, A., Maugeri, M., Lo Presti, D.C.F. and Pallara, O. (1999). Characterising Shear Modulus and Damping from in Situ and Laboratory Tests for the Seismic Area of Catania. Proc of the 2 nd International Symposium on Pre-failure Deformation Characteristics of Geomaterials, Torino, Sept. 1999, pp Cavallaro, A., Grasso, S. and Maugeri, M. (2001). A Dynamic Geotechnical Characterization of Soil at Saint Nicola alla Rena Church Damaged by the South Eastern Sicily Earthquake of 13 December Proceeding of the 15 International Conference on Soil Mechanics and Geotechnical Eng, Satellite Conference Lessons Learned from Recent Strong Earthquakes, Istanbul, 25 August 2001, Cavallaro, A. and Maugeri, M. (2005). Non Linear Behaviour of Sandy Soil for the City of Catania. Seismic Prevention of Damage. A Case History: The City of Catania (Italy), Wit Press Publishers, Ed. Maugeri M. CEN (2003). Design of Structures for Earthquake Resistance. Part 1: General Rules, Seismic Actions and Rules for Buildings, Final Draft. Brussels: European Committee for Standardization (CEN), December 2003, 215 pp. Frenna, S.M. and Maugeri, M. (1995). GEODIN: a Computer Code for Seismic Soil Response. Proceeding of the. 9 th Italian Conference of Computational Mechanics, Catania, Italy, June 1995, (in Italian): pp Giuffrè, A. and Giannini, R. (1982). La Risposta non Lineare delle Strutture in Cemento Armato. Progettazione e Particolari Costruttivi in Zone Sismiche. ANCE-AIDIS. Jamiolkowski, M., Lo Presti, D.C.F., and Pallara, O. (1995). Role of in-situ testing in geotechnical earthquake engineering. Third International Conference on Recent Advances in Geotechnical Earthquake Eng. and Soil Dynamic, State of the Art 7, Vol. 3, pp Lo Presti, D.C.F., Pallara, O, Lancellotta, R., Armandi, M. and Maniscalco, R. (1993). Monotonic and Cyclic Loading Behaviour of Two Sands at Small Strains. Geotech. Testing Journal, Vol. 16, No. 4, pp O.P.C.M. No (2003). Primi Elementi in Materia di Criteri Generali per la Classificazione Sismica del Territorio Nazionale e di Normative Tecniche per le Costruzioni in Zona Sismica. Ordinanza del Presidente del Consiglio dei Ministri, Rome, Italy, 2003 (in Italian). Pastore V. and Turello R. (2000). Geotechnical zoning of the urban area of Catania for earthquake engineering purposes. In Faccioli and Pessina (eds), The Catania Project: Earthquake Damage Scenarios for a high risk area in the Mediterranean, 23-30, Roma: CNR-Gruppo Nazionale per la difesa dai terremoti. Priolo, E. (2000). 2-D Spectral Element Simulations for a Catastrophic Earthquake. In: The Catania Project: Earthquake Damage Scenarios for a High Risk Area in the Mediterranean, pp.67-83, Roma: CNR-GNDT. Vucetic, M., Dobry, R. (1991). Effect of soil plasticity on cyclic response. Journal of Geotechnical Engineering, Vol. 117, No. 1, pp Yokota, K., Imai, T. and Konno, M. (1981). Dynamic Deformation Charact. of Soils Determined by Lab. Tests. OYO Tec. Rep. 3, pp