The impact of active and capable faults structural complexity on seismic hazard assessment for the design of linear infrastructures

Abstract. Since Active and Capable Faults (ACFs) may generate significant permanent deformation of the topographic surface, a careful evaluation of their spatial and geometric characteristics is essential for seismic hazard assessment when planning new linear infrastructures (e.g., roads, railway lines, pipelines). Although this is generally overlooked, the common structural complexity of fault zones leads to a non-uniform hazard along and across faults' traces, because of deformation partitioning. This study reviews the factors controlling fault rupture and propagation, specifically focusing on fault zone architecture and growth mechanisms. Four scenarios of physical interaction between ACFs and linear infrastructures are analysed. The fault-crossing scenario is likely the most susceptible to ground surface displacement, while the fault-parallel scenario needs evaluation of the width of fault damage zone overlapping with the infrastructure. Near-fault tip and transfer zone-crossing scenarios require specific assessment of the local deformation patterns. Given the importance of a structural geological approach toward the reliable assessment of seismic hazard related to ACFs, we review suitable investigations to derive appropriate deterministic geological constraints on the geometry, kinematics, slip and deformation style of ACF's. Our approach may have significant impact on the legislation regulating the early stages of infrastructural design.