## 3 Results
### Local 1D Velocity Models and Location of the Seismic Catalogue
Moving to the SE, in the region of Matala-Central Ptolemy Trench (sub-region 3), significant differentiation is observed in the velocity structure of the crust compared to the one calculated by [39]. More specifically, the final model consists of five layers and a half-space at the same depths as the study by [39], with the noticeable difference situated in the P wave velocities and a significantly lower V\({}_{\rm P}\)/V\({}_{\rm S}\) ratio. The velocity model of the crust varies between 4.9 and 6.8 km/s for approximately 25 km, while the respective values for the neighbouring area of Rethymno are between 5.6 and 6.8 km/s for crustal thickness of less than 31 km (Figure 6b,c). The velocity model of Matala-Central Ptolemy Trench was tested in the recent earthquake sequence near Matala (17 May 2023-31 May 2023), where more than 130 events were located with a better concentration near some of the most significant local fault sources [13; 52] and yielded improved error uncertainties compared to the initial model of [39]. In the central part of the island, the velocity model is divided into more layers (six layers) with approximately the same values of P velocity and crustal thickness. However, the V\({}_{\rm P}\)/V\({}_{\rm S}\) ratio changes from Rethymno (1.76) to Matala (1.74) and Heraklion (1.75) area (Figure 7b-d). The existence of a thick layer of recent deposits (Neogene to Quaternary) above the Alpine basement and the presence of a low-angle subducting lithosphere in the area may explain the reason of the complexity of the local velocity. Our results show a fair correlation with the ones of [53] for the uppermost (<10 km) part of the crust. Precisely, that study estimated a P-wave velocity between 4.8 and 5.5 km/s. Further to the east, in the sub-regions of SE Crete-Pliny Trench and Zakros-Karpathos, the velocity model is simplified to approximately four (4) layers and a crustal thickness of 32-33 km (Figure 6e,f) due to the absence of clear minima during the process of defining the velocity and ceiling depth of the half-space. This result converges with the respective ones of [39; 48] for the same territory in quantity, ceiling depth of the discontinuities (\(\pm\)2 km), and the velocity of each layer (\(\pm\)0.2 km/s). The updated catalogue shows a better concentration of shallow seismic events along the main fault zones of the study area (Figures S1-S12) and minor spatio-temporal errors (Table 1). The higher V\({}_{\rm P}\)/V\({}_{\rm S}\) ratios of the South Cretan Sea (sub-region 5; 1.77) and Eastern Crete-Karpathos Island (1.76) than the respective ones in sub-gions 3 and 4 may reflect the effect of the upward migration of fluids as a result of the dehydration of the subducting sediments within the oceanic origin Tethys plate [54; 55; 56; 57; 58], like in comparable cases [59; 60; 61; 62]. Specifically, this V\({}_{\rm P}\)/V\({}_{\rm S}\) increase may be attributed either to the penetration of water fluids through local faults and flat cracks, saturating the hosting rock formation, or an upward migration of aqueous fluids derived by slab dehydration in the deeper parts of the crust (>10 km), circulating along the main fault zones of the area, fitting most of the observations on local seismic activity and previous studies of earthquake tomography in the region [45]. The subduction of the Tethys oceanic lithosphere under the Aegean microplate causes overlapping velocities, as shown in studies using earthquake, seismic, and gravity data [1; 39; 46; 48; 49; 53]. This overlapping makes it challenging to create local 1D velocity models for each plate separately.