## 4 Discussion  
During the process of PSHA, two types of uncertainties must be considered, i.e., the aleatory and the epistemic uncertainty [94]. The former accounts for the stochastic variations in PGA, PGV, and S\({}_{\text{a}}\) values arising from the implementation of a GMPE, whereas the latter pertains to the accuracy of these values [94]. To address epistemic uncertainties, a logic tree approach is commonly utilized, which involves the incorporation of multiple GMPEs to account for the variability in predictions [93; 94; 95]. In the present work, a non-equal logic tree was constructed to account for both crustal and slab tectonic settings. Two seismotectonic models, namely, EBIM13 and ESHM20, were integrated into the logic tree as area sources to introduce variability. Additionally, multiple GMPEs were utilized to estimate ground motions in terms of PGA and PGV in each area source of the major crustal branch of the logic tree. Taking into account the different focal mechanism types through the implementation of weighted GMPEs, we could establish multiple logic tree paths per area source, resulting in a multi-branch logic tree. The suitability of the pre-selected regional GMPEs, based on the _LLH_ approach, was assessed with the use of a compiled strong motion dataset contained in the study area. The goal of this procedure was to minimize expert judgement and avoid assigning equal weights to all GMPEs, given that differences among them can be found from a simple residual analysis. The relative ranking between the GMPEs was expressed through a weighting equation, taking into account their respective _LLH_ scores. From this analysis, slight differences were found among the candidate GMPEs. Focusing on PGA, SAKK2016 and CHOU2018 performed better than the others in predicting the observations, whereas MARG2002 was assigned the lowest relative weight. The same applies to PGV predictions but with the absence of SAKK2016, which does not have a functional form for PGV, and  
Figure 7: (**a**) PGA hazard curves for Athens, Methana, and the capitals of Salamina, Aegina, Poros, Hydra, Spetses, Kythira, and Antikythira Islands. (**b**) UHS for the aforementioned sites. The red rectangle signifies the range of eigenperiods of most buildings in the study area. Both hazard curves and UHS were constructed considering the soil conditions of each site. with the remaining GMPEs apart from MARG2002 being assigned almost equal weights. An overarching comment could be that most recent GMPEs seem to be more effective in forecasting strong ground motion regarding the administrative region of Attica. This is well reasoned given that as we move further back in time, the strong motion data available for that time decrease. The PGA distribution for a return period of 475 years was directly compared to the PGA reference values set by the current Greek Building Code [96]. EAK2003 partitions Greece into three distinct PGA zones and prescribes a reference value of peak acceleration for a return period of 475 years. The study area is classified into zones I and II of EAK2003, with reference values of 0.16 g (~160 cm/s\({}^{2}\)) and 0.24 g (~240 cm/s\({}^{2}\)), respectively. Specifically, sub-areas 1, 2, 3, and 5 belong to zone II, whereas sub-area 4 (Hydra and Spetses) is part of zone I. Seismic hazard analysis of sub-area 1 (Attica peninsula) revealed that the PGA contour of 240 cm/s\({}^{2}\) is situated in the western part of the group's mainland, near the Gulf of Corinth, highlighting the substantial impact of the Gulf's past strong events on the peak ground motions at western Attica. The maximum PGA value observed in sub-area 1 was approximately 300 cm/s\({}^{2}\), located at the westernmost part of the study area, which is 60 cm/s\({}^{2}\) higher than the EAK2003 regulations. Notably, the Attica peninsula displayed the highest and lowest PGA values among all groups. This contradiction can be attributed to the extent of Attica and the characteristics of seismicity in neighboring areas.