## 4 Seismic Analysis
### Seismic Inputs  
The soil characteristics at the hospital's location were obtained using the USGS global \(V_{8,30}\) map along with previous local \(V_{8,30}\) studies conducted in the province of Alicante. According to [PERSON] et al. (2011) [45], the soil beneath Vega Baja Hospital is predominantly composed of soft, highly malleable clay. Based on the ground classification in clause 3.1.2 of Eurocode 8 [46], the soil is categorised as type D with a time-averaged shear-wave velocity (\(V_{8,30}\)) of less than 180 m/s at a depth of 30 m.  
The Iberian Peninsula experiences relatively low to moderate seismic activity compared to other regions worldwide with frequent earthquakes typically having a moment magnitude (\(M_{\rm w}\)) below 5.5. The southern and southeastern parts of Spain are particularly prone to higher seismic hazards within the country [47; 48] with peak values reaching 0.23 g for a 10% probability of exceedance over 50 years (equivalent to a return period of 475 years). Although Spain is generally classified as a moderate to low seismic risk area compared to other European countries such as Italy or Greece, it has still experienced significant earthquakes in the past, notably the 1829 Torrevieja earthquake and the 1884 Arenas del Rey earthquake, both of which had maximum intensities of IX-X on the EMS-98 scale [49]. In the past 25 years, southeastern Spain has experienced seven earthquakes with moment magnitudes exceeding 4.5 with the 2011 Lorca earthquake standing out as it caused considerable damage to buildings and resulted in injuries. In most applications of Eurocode 8 [50], a seismic hazard is represented by a single parameter: the reference peak ground acceleration on type A ground, which is denoted as \(a_{\rm gR}\) or PGA. This study analyses two limit states: the Serviceability Limit State (SLS), also referred to as Damage Limitation (DL), which has a higher probability of occurrence \begin{table}
\begin{tabular}{c c} \hline
**Load Type** & **Value (kPa)** \\ \hline Self-weight & 3.63 \\ Dead load & 2.45 \\ Live load & 3.43 \\ \hline \end{tabular}
\end{table} 
Table 8: Applied load on the first and second floors of the case study. \begin{table}
\begin{tabular}{c c} \hline
**Load Type** & **Value (kPa)** \\ \hline Self-weight & 3.63 \\ Dead load & 3.92 \\ Live load and snow & 1.96 \\ \hline \end{tabular}
\end{table} 
Table 9: Applied load on the third floor and the stairs roof of the case study. during the design life (e.g., 10% probability in 10 years with a return period of 95 years), and the Ultimate Limit State (ULS), representing Severe Damage (SD), which has a lower likelihood of occurrence (e.g., 10% probability in 50 years with a return period of 475 years). According to updated seismic hazard maps [48], the selected PGA values for these limit states are 0.12 g for SLS and 0.21 g for ULS. The elastic response spectra for this case study, based on soil type D and importance class IV (hospital) as per EC8, are shown in Figure 9 for the two limit states (SD and DL, with PGA values of 0.21 g and 0.12 g, respectively). These spectra are presented as relationships between period and spectral acceleration. In nonlinear time-history analysis, the selection of ground motion characteristics plays a crucial role in influencing the results, requiring careful consideration during the record selection phase [51]. To evaluate the performance of the three-dimensional case study building under seismic conditions, two acceleration time-history records were applied along the primary horizontal directions of the model, namely X and Y. For a reliable estimation of the hospital building's seismic response, two distinct sets of ground motions with their respective scaling factors (see Tables 10 and 11) were chosen.