## 3 Ground Motion Selection  
The Republic of Croatia is located in the Mediterranean-Transasian seismic belt, characterized by high seismic activity. This has led to several major earthquakes throughout its history. It is estimated that 5.53% of Croatia's total land area is exposed to the possibility of earthquakes with a peak ground acceleration (PGA) of 0.3 g or higher, encompassing approximately 21.02% of the country's population. Furthermore, earthquakes with PGA values ranging between 0.2 g and 0.3 g could impact 30.89% of the territory, housing 41.66% of the population. For more than half of Croatia's territory, earthquakes with PGA values between 0.1 g and 0.2 g are expected, affecting over a third (1,633,529) of the total population [31]. To illustrate seismic hazards for the most vulnerable cities, a predictive model was developed [31] to assess the vulnerability of buildings across 429 municipalities and 127 cities in Croatia. Building vulnerability levels were calculated from 0.5 to 1.0, with intervals of 0.1, correlating these values with peak ground acceleration (Figure 3). The study identified 32 Croatian cities ranging from the most to the least vulnerable to seismic events. Zagreb, the capital city, has an expected PGA value of 0.26 g. It is estimated that 90.2% of buildings in Zagreb would be affected by such seismic events. For Dubrovnik, where the expected PGA is 0.3 g, the situation is more critical, with approximately 95% of buildings projected to be affected. Figure 3: Seismic hazard distribution in Croatia [31]. The selection of seismic records in this study was conducted using a uniform hazard spectrum (UHS) [32] and disaggregation for the observed cities: Zagreb and Dubrovnik (Figures 4 and 5). The UHS represents acceleration spectra relative to oscillation periods for a given location, ensuring the equal probability of exceedance for a specified return period. The UHS is more reliable and precise than the generalized smoothed spectrum defined by EN 1998-1:2004 [33] as it accounts for all characteristics of a specific location. For the cities under analysis, disaggregation is defined based on the expected structural period of existing buildings and desired return period. Disaggregation separates the effects of various seismic activities affecting the area, producing graphical representations of magnitude (M) and epicentral distance (R) ranges. These values guide the selection of seismic records from [34]. Based on the defined ranges of magnitude (M) and epicentral distance (R) corresponding to the area of the cities of Zagreb and Dubrovnik, determined through disaggregation, 30 earthquake records were selected to simulate the potential seismic hazard of the area. The magnitude and epicentral distance values represent the boundaries, while for the selected earthquakes in the scenario for Zagreb, the magnitude and distance values are shown in Figure 6a. The figure indicates that most epicentral distances (Rs) are up to 25 km,  
Figure 4: UHS with return period of 475 years and magnitude range (M) and epicentral distance (R) for Zagreb [32]. Figure 5: UHS with return period of 475 years and magnitude range (M) and epicentral distance (R) for Dubrovnik [32]. while the majority of earthquake magnitudes fall between 4.5 and 6, with two outlier values. Figure 6b illustrates the mean ground acceleration for the 30 selected earthquake records, which is 2.60 m/s\({}^{2}\), corresponding to the peak ground acceleration value of 0.26 g observed previously. This demonstrates the consistency between the initial and final selected parameters used to define the seismic scenario for Zagreb. Figure 6c,d show that most of the R values are within 60 km, with one outlier, while the majority of earthquakes have magnitudes between 4.5 and 6, with an average ground acceleration value for the 30 selected earthquake records, which is 3.00, corresponding to the observed peak ground acceleration value of 0.30 g for Dubrovnik.