# GIS-Based Optimal Route Selection of Submarine Cables Considering Potential Seismic Fault Zones
## 4 Discussion
In general, the length (and consequently the cost) of submarine cables is directly related to the depth at which they are laid. However, submarine cables that are laid at shallow depths (up to 300 m) are frequently exposed to the geohazard of slope instability (under static and/or seismic conditions), as almost 30% of cable structural damages are related to seabed slope failure [71]. Apart from the issuesrelated to structural integrity, a large seabed inclination might considerably increase the cable cost [72]. Hence, a rating score that increases with the increase of bathymetry and seabed inclination has been assigned. It is worth noting that in practice, cables crossing steep seabed slopes are commonly laid perpendicular to the slope in order to reduce their contact surface area with the seabed [24]. Figure 9 illustrates the reliability and effectiveness of the developed decision-support tool. An optimal route has been derived from the application of the smart tool and is compared with the route of a real engineering project, namely the EuroAsia Interconnector. The proposed route is almost identical to the EuroAsia routing, while the differences observed in the central and eastern parts might be attributed to the lack of data (i.e., topographic survey, geotechnical study, etc.) and further information regarding the actual project's routing (i.e., weight values, rating scores, etc.). Figure 10a,b are related to Case Study 1, i.e., the telecommunication cable connecting Crete to Libya. Route I is based on the realistic scenario and crosses almost vertically the critical fault zones of the Hellenic trench and Herodotus trough, while inevitably passing through the areas characterized by steep slopes (i.e., near the island of Crete and near the coasts of Libya). However, the length (and cost) of Route I is minimized within these potentially dangerous areas (due to vertical crossing). Route II, where seabed inclination has been assigned high weight values, is very close to Route III, where seismic fault zones have been set highly influential. Both Routes II and III cross the critical fault zones with a perpendicular orientation, whereas the latter constitutes the shortest among the proposed alternative routings. Route IV corresponds to the intermediate scenario and it can be clearly seen that the medium effect of bathymetry has played a key role. Although Route IV has successfully avoided deep and ultra-deep waters, its length is considerably increased and passes through the steep slopes located near the island of Crete. It is noted that the Hellenic trench is crossed at an angle different than 90\({}^{\circ}\). The 457 km-long Route V is dominated by the effect of bathymetry and constitutes the longest route. An extensive part of Route V passes through the steep slopes near Libya and Crete, whereas the critical fault zones are not vertically crossed. In addition, it can be easily observed that the existing cable route is almost straight, crossing for several kilometers the dangerous zones near the Cretan coastline, and consequently, it is susceptible to the geohazard of earthquake-triggered submarine landslides. Proposed Routes I, II and III differ from the existing cable in the way they pass through the potentially unstable zones, as well as the crossing of the Hellenic trench. Figure 13a,b refer to Case Study 2, i.e., the power cable connecting the island of Crete to Egypt. Route I, where the weight value of bathymetry has been set equal to 82%, constitutes the longest proposed route (i.e., 555 km long) and differs significantly from the other proposed routings. This is attributed to the fact that deep and ultra-deep waters have been rated higher, compared to shallower depths, and consequently Route I has avoided the deep waters north of Egypt. The low influence of seabed inclination and seismic fault zones has led Route I to pass through an extensive zone of a large seabed inclination (\(>\)30\({}^{\circ}\)), and cross, at an angle different from 90\({}^{\circ}\), the Cretan-Rhodes ridge and the Hellenic trench.