## 3 Results
### Relative Locations (hypoDD) of the Seismic Catalogue  
In this study, more than 4500 events of M\({}_{\rm L}\geq 2.2\), comprising 69,201 phases, were relocated with hypoDD (Figure S13). The procedure of the relative hypocentral relocation was performed for each sub-region (1-6) separately, using the local velocity models and V\({}_{\rm P}\)/V\({}_{\rm S}\) ratio described in the previous section. Due to the size and the large number of seismic events in each area, the hypoDD relative locations were estimated using the LSQR method, which may under-estimate the respective errors. The damping parameter for each area was set to different values in order to produce condition numbers between 40 and 80 for relocated clusters as suggested by [43]. A total of 4113 events were successfully relocated (\(\sim\)89%) with an average RMS residual of 0.18 s, which is significantly lower than the respective one of the absolute locations obtained with HYPOINVERSE, which is 0.30 s. The lack of fidelity in these error estimations led us to divide the data into even smaller clusters in order to produce more accurate location uncertainties using the singular value decomposition (SVD) method [43]. Then, the catalogue was merged and the average obtained uncertainties for each sub-region are shown in Table 2. In Figures 8 and 9, the displacement between the epicentre locations obtained using the single-event (HYPOINVERSE) and the double-difference (hypoDD) algorithms as well as the depth distribution between the initial and the final catalogue is shown in both map projection and histogram graph. In the westernmost region (Antikythera-Chania), 652 out of 683 events of the initial locations (M \(\geq\) 2.2) were relocated with HYPODD, giving a first result that could be rated as satisfactory. The calculation of differential travel times resulted in an average number of seven links per event pair and an average offset between the linked events of 3.37 km. There were approximately 29% weakly linked events and 0.5% strongly linked events. The relocated seismic events (supplementary material) are mainly concentrated in the N-S striking normal faults west of Kissamos gulf, and some smaller clusters are located south of Crete, along the HT, or near Kythera-Antikythera in greater depths (H \(\geq\) 30 km). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Area ID**} & \multicolumn{2}{c}{**Total Number of Earthquakes**} & \multicolumn{1}{c}{**Centroid**} & \multicolumn{1}{c}{**Centroid**} & \multicolumn{1}{c}{**ErrX**} & \multicolumn{1}{c}{**ErrY**} & \multicolumn{1}{c}{**ErrZ**} \\  & **(Sum of Smaller Clusters)** & **Lat** (\({}^{\circ}\)**N) & **Lon** (\({}^{\circ}\)**E) & **Depth** (km) & **(km)** & **(km)** & **(km)** \\ \hline
1 & 652 & 35.57 & 23.48 & 7.49 & 2.2 & 2.5 & 4.8 \\
2 & 578 & 34.98 & 24.05 & 11.46 & 0.7 & 0.8 & 0.9 \\
3 & 110 & 35.02 & 24.83 & 5.53 & 1.8 & 0.6 & 1.2 \\
4 & 1974 & 35.15 & 25.26 & 10.35 & 0.5 & 0.8 & 1.0 \\
5 & 615 & 34.71 & 25.36 & 18.02 & 2.2 & 1.0 & 3.6 \\
6 & 799 & 35.58 & 26.31 & 21.37 & 0.5 & 1.6 & 2.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Statistics of spatial errors and centroid coordinates and depth for each sub-region using the SVD method to assess the relative relocation uncertainties. Figure 8: Histogram of the absolute frequency (log scale) of the displacement between the located and the relocated events in km. In the area of Rethymno (sub-region 2), 578 out of 656 events of the initial catalogue (M \(\geq\) 2.2) were relocated with hypoDD, improving the concentration of the earthquakes along main faults. The calculation of differential travel times resulted in an average number of seven links per event pair and an average offset between linked events of 2.93 km. The earthquakes of the relocated catalogue are mainly concentrated in the E-W striking thrust offshore faults south of Crete, and some sparser clusters, related to the activity of the HT, are located in the area \(\sim\)30 km SSW of Crete, in the vicinity of Gavdos Island (supplementary material).