# 2-D Seismic Response Analysis of a Slope in the Tyrrhenian Area (Italy)
## 4 Discussion and Conclusions  
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 quantification of the risk of instability phenomena, such as landslides or liquefaction triggering. In this paper, a study on the evaluation of the topographic effects for a slope in the Tyrrhenian area of Southern Italy has been carried out. Detailed geotechnical characterization was also carried out by in situ and laboratory tests. The laboratory tests performed in the static field made it possible to evaluate the mechanical characteristics of the soil, allowing to obtain the fundamental parameters as a function of depth such as unit weight, moisture content, Atterberg limits, void ratio, porosity and degree of saturation; moreover, through direct shear tests it was possible to obtain the values of the cohesion and the angle of shear resistance. The laboratory tests performed in the dynamic field allowed for evaluating the non-linear behavior of soils in terms of stiffness attenuation with strain G/G\({}_{\text{o}}\)-\(\gamma\) and the damping ratio evolution with strain D-\(\gamma\). Moreover, the results obtained through the Down Hole (DH) tests made it possible to derive the trend with the depth of the shear wave velocity and other parameters such as the Poisson ratio and the coefficient of earth pressure at rest. The definition of seismic action was based on synthetic seismograms related to the 1908 Messina and Reggio Calabria earthquake and the 1693 Val di Noto earthquake. A numerical model based on the 1-D EERA and 2-D QUAKE/W codes was performed for the slope model in the Caronia area, subjected to vertically propagating in-plane shear waves (V\({}_{\text{s}}\) waves). Results show that stratigraphic amplification and topographic amplification effects were found to interact, suggesting that to accurately predict topographic effects the two effects should not be always handled separately. 1-D computer codes have been used to model the equivalent-linear earthquake site response analyses of layered slope deposits, as generally performed by professionals. Because the slope is moderate (average slope angle is i = 22\({}^{\circ}\)), a 1-D response analysis, often used by professionals, was the first step of the study, as indicated by the provisions of national and international building codes. Besides, the local seismic response analysis has been also performed in greater detail using a counted 2-D simple model. Results show amplification of the seismic motion using initially the 1-D code. Besides, by performing the 2-D analysis, further amplification of the seismic acceleration at the crest of the slope was found. By the numerical analyses, three points in the slope cross-section were monitored as follows: point 1 located behind the crest of the slope; point 2 located at the crest of  
Figure 24: Comparison between elastic response spectra at the crest (1-D and 2-D) and behind the crest (2-D), for the [PERSON] et al. [26] input. the slope; point 3 downstream sufficiently far from the foot of the slope. This result is in agreement with the [PERSON] and [PERSON] [46] approach, as shown in Table 8, where the values of the topographic amplification are presented. An average value of the topographic amplification \(A_{t}=0.22\) was observed, with a maximum value of \(A_{t}=0.65\) using as an input motion the [PERSON] 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 Topographic Aggravation Factor (TAF) were also computed. The evaluation of the Topographic Aggravation Factor (TAF), after the [PERSON] et al. [48] approach, shows values of TAF reaching on average about 1.45 in the frequency range f of 1-5 Hz.