Accessibility risk assessment under Cascadia Subduction Zone earthquakes: case study on hospital accessibility in Portland metro area

A resilient transportation network is critical for maintaining access to emergency services following natural disasters.This study quantifies hospital accessibility risk in Portland Metro Area from a magnitude 9 Cascadia Subduction Zone earthquake scenario.The transportation network is modeled as a graph consisting of 1,756 nodes and 2,639 links, including 664 bridges located on 461 of the links.Accessibility is measured using Hansenbased metric, and indirect risk is quantified as the expected loss in accessibility resulting from bridge failures.To efficiently estimate network risk and identify critical assets, a Transitional Markov Chain Monte Carlo sampling framework is employed.The results indicate that the analyzed earthquake scenario could cause an approximately 12% loss in hospital accessibility.Additionally, fragility models with two different levels of complexity were investigated to demonstrate the effects of fragility simplification on (a) the network-level risk and (b) the ranking of critical links.The comparison reveals that an overly simplistic fragility model may underestimate the network-level risk by about 31%, and it may also deliver drastically different rankings for critical links.