Geologically, Oregon is located in the Cascadia Subduction Zone (CSZ), making it subject to some of the world’s most powerful, recurring earthquakes. The last major quake in Oregon occurred 317 years ago, a timespan that exceeds 75% of the intervals between the major quakes to hit Oregon over the last 10,000 years. There is a significant risk that the next event will occur soon. Such an earthquake will cause major ground shaking, settling and landslides causing widespread damage to buildings, utilities, and transportation facilities.*
None of the older downtown bridges (including the I-5 Marquam and I-405 Fremont bridges) are expected to be operational after a major Cascadia Subduction Zone earthquake.
To get a better understanding of what we would experience locally from a major Cascadia Subduction Zone earthquake, we are working with a team of experts that include local geotechnical and structural engineers that are licensed and work in the northwest to develop anticipated shaking levels based on soils at the site, U.S. Geological Survey Science data and modelling. We are also looking at recent examples of subduction zone earthquakes and affected cities that share similar distances from the fault line or rupture zone, such as Tokyo, Japan and Santiago, Chile.
Based on local data from our known faults and data collected during other similar earthquakes around the world including California, Mexico, Chile, and Japan, engineers and geologists have been studying and developing shaking models over the last several decades. The models are often updated with new data and science as earthquakes happen, research continues, and technology changes. This work has been completed by local engineers, researchers, and those at prominent universities on the west coast.
* The Oregon Resilience Plan. Report to the 77th Legislative Assembly. 2013
This shows recent subduction zone earthquake events, the extent of their levels of shaking, and pictures of damage experienced.