# Horizontal PGA Estimates for Varying Deep Geological Conditions--A Case Study of Banja Luka
## 4 PSHA Analysis for the Case Study Location in Banja Luka  
Using Equation (3) as the GMPE and the SHARE Project's pan-European seismic source zone model [83, 84, 85], we performed a PSHA analysis for the site with coordinates \(44^{\circ}46.5^{\prime}\) N, \(17^{\circ}15^{\prime}\) E, denoted by the solid blue circle in Figures 1 and 4. The PSHA analysis will be based on [PERSON]'s [86] and [PERSON]'s [87] approaches and will adhere to [PERSON] et al. 's [88] procedure. For all hazard calculations, we used the REASESS V2.1 software [88]. The total hazard is the sum of the contributions from each source zone, \(i\) (from the full set of zones, \(I\)). Figure 4 depicts the borders of the selected seismic zones used for hazard calculations in this research. Although not the subject of this investigation, seismic source zones can be established using publicly accessible regional seismological data [89, 90, 91]. In this particular study, we use the source zone model that was based on the new homogeneous earthquake catalogue (\"SHARE European Earthquake Catalogue\"--SHEEC [92]), created for the scope  
Figure 3: The horizontal PGA values recorded at four separate accelerograph stations in Banja Luka, compared to the median and median \(\pm\)\(\sigma_{\text{log}}\) empirical horizontal PGA estimates derived using Equation (3). The 95% confidence interval (median \(\pm\)\(2\cdot\sigma_{\text{log}}\) empirical PGA estimates) is displayed by the gray area. of the SHARE Project. The SHEEC catalogue's completeness, homogeneity of magnitudes with respect to \(M_{W}\), and other significant aspects are explained in depth in [84; 93; 94]. Figure 4 displays the source zones included in the hazard calculations for Banja Luka. The two larger circles, with radii of 111.75 and 81.75 km, represent the source-to-site distances that must be included in the PSHA computations to ensure 1% accuracy of computed PGA estimates with a probability of 10% in 10 and 50 years (the 95- and 475-year return periods), respectively. The two smaller circles, with radii of 57.75 and 40.00 km, indicate the maximum distances that will ensure a PSHA accuracy of 10% for the same two probabilities. Figure 4 also depicts the epicenters of several of the major historical earthquakes as well as a few recent disastrous earthquakes in the northwestern Balkan region [34]. As illustrated in Figure 4, local seismicity dominates in the PGA probabilistic estimates, and only the \(M_{W}\) = 6.1 1969 Banja Luka earthquake and \(M_{W}\) = 6.4 2020 Petrinja earthquake are within the depicted radii, while all other shown events occur in areas that do not significantly contribute to the seismic hazard. It is also worth mentioning that some recent regional studies have found that PGA amplitudes are primarily influenced by local seismicity and are not particularly affected by very strong and distant events, such as those in Romania's Vrancea source zone [61; 63; 64; 65; 96]. This is because high-frequency seismic waves attenuate rapidly. As a result, while traveling from great distances, their final contribution is less than that of the waves created by local events. Seismic microzonation studies for the cities in Serbia and North Macedonia that are all closer to the Vrancea zone than Banja Luka demonstrate that the contribution of Vrancea earthquakes to PGA values is negligible when compared to local seismicity [61; 63; 64; 65]. As a result, in this study, we will also overlook the Vrancea source zone. Figure 4: The SHARE Project earthquake source zones [83; 84; 85] used in this research for seismic hazard assessments.