## 5 Conclusions  
With a population of around 180,000, Banja Luka is the cultural and financial center of the Republic of Srpska and the second most populated city in Bosnia and Herzegovina. The city is located between the Pannonian Basin and the Dinaric Alps and has scattered outcrops of geological rocks as well as areas of complex deep geology, in addition to areas with deep geological sediments. The city was struck by the catastrophic \(M_{\rm W}\) = 6.1 Banja Luka earthquake on 27 October 1969, when 60% of all buildings were damaged beyond repair [64]. This demands a constant re-evaluation and update of Banja Luka's seismic hazard estimations, including vertical PGA values. Regional attenuation equations for vertical PGA are first described, and then PSHA analyses were done using these GMPEs, which take into account both local soil conditions and deep geology. Despite the small number of accelerograms from the northwestern Balkans utilized to produce the GMPEs, the empirical estimates are highly consistent with observed intensities in Banja Luka. The most important findings of this study can be summarized as follows:  
Figure 7: A comparison of the _PGAvert_ values for the location with coordinates 44\({}^{\circ}\)46.5\({}^{\prime}\) N, 17\({}^{\circ}\)15\({}^{\prime}\) E, in Banja Luka, calculated for different return periods, to the PGAs based on current official hazard maps for Bosnia and Herzegovina [34] and the VHPga suggested by Eurocode 8 [1]. _PGAvert_ estimates based on the macroseismic intensity degrees from ex-Yugoslav mays [38] are also shown. * Site conditions have a significant impact on the vertical PGA,
* The deep geology effects are even greater than the local soil effects,
* VHpga values are influenced by deep geology, local soil, source-to-site distance, and the probability level of empirical estimates,
* Only the combination of stiff soil and deep geology rocks may produce a median empirical vertical PGA equivalent to that associated with VIII \({}^{\circ}\)MCS, which was the predominant intensity of the 1969 Earthquake in Banja Luka,
* Vertical PGA probabilistic hazard estimates are dominated by local seismicity. Furthermore, we should mention that the latest official (2018) hazard maps [34] provide PGA estimates that are comparable to our estimates of horizontal PGA for Banja Luka. It will be possible to obtain considerably better GMPEs only if the number of strong motion records in this region is increased. Until then, our results can be seen as a first step toward more realistic PHSA estimates for Banja Luka. Conceptualization, B.B., S.L. and S.B. ; methodology, B.B. and S.L. ; formal analysis, B.B., S.L., S.B. and M.K. ; investigation, B.B., S.B., A.S.-C. and M.S. ; data curation, B.B. ; writing--original draft preparation, B.B., S.L., S.B. and M.H.-N.; writing--review and editing, B.B., S.L., S.B., A.S.-C., M.S. and M.H.-N.; visualization, B.B. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The original contributions presented in the study are included in the article, further inquiries can be directed to the authors. The authors would like to thank the two anonymous reviewers for their insightful comments and suggestions, which lead to a significantly improved manuscript. For the first, third, fourth, and fifth authors, this research has been supported by the Ministry of Science, Technological Development and Innovation (Contract No. 451-03-137/2025-03/200156) and the Faculty of Technical Sciences, University of Novi Sad, through the project \"Scientific and Artistic Research Work of Researchers in Teaching and Associate Positions at the Faculty of Technical Sciences, University of Novi Sad 2025\" (No. 01-50/295). The authors declare no conflicts of interest. The following abbreviations are used in this manuscript: