## 4 Discussion and Conclusions
Abbreviations—ECG: Eastern Corinth Gulf; ThrM: Thracomacedones; TNF: Thiriassion Normal Fault; FyNF: Fyli Normal Fault; PNF: Palaiokoudoura Normal Fault; MFZ: Menidi Fault Zone; KFZ: Kamatero Fault Zone. In addition, a WNW-ESE trending zone of negative S-wave velocity anomalies was also observed at 5 km depth on the eastern edge of the region, potentially linked to offshore faults. At 20 km depth, a positive anomaly extending from the Athenian plain to the Eastern Corinth Gulf, coinciding with a change in the fault direction, was also observed. The 3-D seismic velocity models and \(\rm V_{P}/V_{S}\) ratio are generally well correlated with medium- to large-scale faults. The study provided a high-resolution 3-D crustal velocity structure in Attica and neighboring regions. The observed velocity anomalies and patterns offer insights into the region's tectonic evolution which may be used in future seismic hazard studies. The correlation between the obtained body-wave velocity structure and local faults can help identify areas of increased seismic activity. The LET has revealed interesting contrasts in the epicentral region of 1999 and 2019 aftershocks by analyzing the distribution of body-wave velocity perturbations as well as the \(\rm V_{P}/V_{S}\) ratio in both horizontal slices and vertical profiles. The presence of velocity anomalies in this region suggests a possible continuation towards the W-NW of the causative fault. This may have played a key role in the relatively surprising 2019 event, which occurred 20 years after the Mw = 6.0 earthquake that caused severe damage in the metropolitan area of Athens and its suburbs. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app14156427/s1](https://www.mdpi.com/article/10.3390/app14156427/s1)]([https://www.mdpi.com/article/10.3390/app14156427/s1](https://www.mdpi.com/article/10.3390/app14156427/s1)): Figure S1: Geological map of Attica and neighboring areas. Toponyms are the respective ones we see in Figure 2; Figure S2: Total P- (blue) and S-ray (yellow) distribution; Figures S3 and S4: Normalized ray density of P- and S-waves; Figures S5 and S6: Distribution of P- and S-rays in the performed cross-sections; Figures S7-S9: Reconstruction of \(\rm V_{P}\), \(\rm V_{S}\), and \(\rm V_{P}/V_{S}\) for the depth slices of 5, 10, 15, and 20 km and cell size of 10 km; Figures S10-S12: Checkerboard tests for checking the vertical resolution of \(\rm V_{P}\), \(\rm V_{S}\), and \(\rm V_{P}/V_{S}\); Table S1: Focal parameters of the significant earthquakes of Figure 2. Source: Ref. [26] Significant earthquakes 2003-2024, Seismological laboratory of NKUA. References [7; 24; 26; 38; 49] are cited in the supplementary materials. Conceptualization, A.K. ; methodology, A.K. and F.V. ; software, A.K. ; validation, A.K. and F.V. ; formal analysis, A.K. and F.V. ; investigation, A.K. and F.V. ; resources, A.K. and F.V. ; data curation, A.K. and F.V. ; writing--original draft preparation, A.K. ; writing--review and editing, A.K. and F.V. ; visualization, A.K. ; supervision, A.K. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. All data products generated in this study (velocity models, earthquake catalogs) are available from the authors upon request. We would like to thank the scientists, post-graduate students, and personnel who participated in the installation or maintenance of the stations belonging to the HUSN and assisted with the signal processing and manual location of the recorded seismicity and the two reviewers for their creative comments and suggestions that upgraded the details of this work.