## 5 Conclusions  
High-pressure gas pipelines are highly vulnerable to earthquake-related geohazards (tectonic faulting, slope instabilities, and soil liquefaction phenomena). Since the complete avoidance of such geohazardous areas is not always feasible from a techno-economical perspective, crossing these areas may detrimentally affect the structural performance of pipelines, necessitating expensive and impractical mitigation measures. Thus, selecting cost-effective, safe, and resilient routing is of paramount importance. Optimal route selection, which is one of the main activities when designing critical infrastructure, is characterized by a multidisciplinary and complex nature due to the vast amount of data, as well as the complexities and uncertainties involved. The current work presents a GIS-based decision-support tool that combines in a computationally efficient manner: (a) the advanced capabilities and functionality of GIS for geospatial processing, (b) a multi-criteria decision method that translates the qualitative prioritization of the adopted design criteria into weight factors, and (c) the sophisticated GIS-based LCPA technique that leads to the optimal path between two geographic points. The developed computational tool can be efficiently applied for the optimal route selection of critical infrastructure, taking into account, among other criteria, the presence of earthquake-related geohazards. This tool considers not only standard earthquake-related geohazards but also more complex geohazards, such as secondary fault ruptures being non-parallel or even perpendicular to the main fault, which might not have been fully considered during the design of existing pipelines. The proposed decision-support tool is applied to a particular area in northern Greece. Four different \"geotechnical\" scenarios have been examined considering the presence of earthquake-related geohazards, while a holistic -and more realistic- scenario has been additionally identified, taking into account various design criteria. Several length- and cost-minimized routings are obtained. The application of the computational tool led to the following useful conclusions:  
* The examined area in northern Greece, between the cities of Kavala and Alexandropolis, is prone to earthquake-related geohazards. Both standard and more complex earthquake-related geohazards coexist within a few square kilometers. Thus, the optimal routing of critical infrastructure in such areas constitutes a very demanding and challenging process. * The assigned weight value corresponding to the criterion of slope inclination considerably affected the orientation of the proposed routings. This is evidenced by the fact that almost all of the proposed alternatives resulting from the \"geotechnical\" scenarios pass through the flat area south of the Kavala-Xanthi-Komotini main fault. * Crossing a potentially liquefiable area located near the coast may be additionally unfeasible in engineering applications due to various restrictions associated with the presence of any infrastructure in coastal areas. * Assigning high importance to seismic fault zones, which results in pipeline routings that cross the fault zones almost vertically, has led to up to 8% shorter routes compared to the other examined \"geotechnical\" scenarios. * The route resulting from the holistic scenario is qualitatively compared to the existing route of the Trans Adriatic Pipeline (TAP). Both routes have similar lengths; they completely avoid potentially liquefiable areas while crossing the two considered secondary seismic fault zones. Nonetheless, the proposed routing does not cross the western part of the primary seismic fault zone as it passes through the gentle slopes in the north of the study area. Certainly, automated decision-support tools can considerably facilitate the process of optimal route selection by reducing the probability of failure and life-cycle costs of the examined infrastructure and minimizing the impact of human errors and bias.