An overview of the volcano-tectonic hazards of Portland, Oregon, and an assessment of emergency preparedness

Abstract

Portland, Oregon, lies within an active tectonic margin, which puts the city at risk to hazards from earthquakes and volcanic eruptions. The young Juan de Fuca microplate is subducting under North America, introducing not only arc magmatism into the overlying plate, but also interplate and intraplate seismicity related to the subduction zone. Large crustal earthquakes are also probable in Portland because of the oblique strike-slip Portland Hills Fault zone. These hazards create risk to Portland residents and infrastructure because of pre-existing vulnerabilities. Much of Portland's downtown area, including the government and business districts, is at risk of ground shaking infrastructure damage, liquefaction and landslides due to earthquakes. Additionally, the city is within 110 km of three active Cascadia stratovolcanoes, two of which pose hazards from tephra and lahars. Though the city is under the umbrella of four emergency response plans-city, county, state and federal-there are critical gaps in mitigation strategies, emergency exercises and community education and outreach. Portland cannot prevent earthquakes or volcanic eruptions, but the city can reduce its vulnerability to these hazards.