Liquefaction-induced road closures after a Cascadia Subduction Zone earthquake would not be distributed evenly. A new mechanics-informed fragility model, operating at 90-meter resolution across the National Highway System, finds that impacts concentrate in low-lying coastal zones, river valleys, and urban waterfronts. US Route 101 -- the primary north-south artery along the Pacific coast -- faces disproportionate disruption. Analysis of Washington counties reveals that limited network redundancy amplifies the seismic hazard: communities with few alternative routes lose not just a road but access to hospitals.
The finding also surfaces a correlation between road damage probability and demographic vulnerability. The populations most likely to lose road access are the populations least equipped to compensate for it. This is not coincidence. Low-lying coastal zones and river valleys were historically settled because they were accessible and flat -- the same properties that make soil susceptible to liquefaction. The geography that attracted settlement is the geology that threatens it.
The structural principle is that infrastructure networks inherit the vulnerabilities of their substrates, and those vulnerabilities correlate with the reasons the network was built there in the first place. The most critical links are often the most fragile links, not despite their importance but because the features that made them important -- low elevation, flat terrain, proximity to water -- are the features that make them fail. Redundancy is not a general property of a network; it is a local property that is thinnest precisely where it is needed most.
(arXiv:2603.16948)