Advancing regional analysis of road infrastructure exposure to fault displacement hazard: A New Zealand case study

We developed an approach to quantify road infrastructure exposure to fault displacement hazard (FDH) that adopts Fault Displacement Hazard Analysis (FDHA) principles and addresses regional-scale challenges for emergency management and network planning. FDH results from ground deformation in surface-rupturing earthquakes and can damage nearby infrastructure. This study assesses New Zealand's road network exposure and vulnerability to FDH by generating displacement fields around faults based on historical earthquake data and physics-based models. Relative hazard is quantified as the product of 1D strain resolved along roads and normalised fault slip-rate, and was mapped at the regional scale. Vulnerability is assessed using geomorphon land class, or the road's position in the landscape, as a proxy for susceptibility to damage and repairability. Four areas emerged as potentially having higher risk: Wellington, the Eastern North Island, the West Coast, and the Upper South Island. We reviewed the local factors that influenced these measurements of hazard, exposure, and vulnerability. The Wellington Region is particularly vulnerable where roads intersect the Hutt Valley and Wairarapa Faults, and sections of State Highway 6 along the Alpine Fault in the West Coast are at heightened risk. This analysis underscores the need for regional approaches to fault displacement hazard and for targeted mitigation, such as fault avoidance, engineering solutions, and planning for rapid post-event repair. Our findings provide insights into horizontal infrastructure resilience planning for transport and other critical systems in seismically active areas.