Breathe easier, Cascade Subduction worriers. Since the discovery of the potential M9 earthquake, the Cascadian Subduction Zone has driven much of the planning in the Portland-Vancouver area. It has entered, as a major factor, in transportation system planning. At worst is the charge that some area structures may just “fall in the water” someday.
We know the West Coast is seismically active. What has become clearer due to major scientific studies is that the likelihood of a major, deep earthquake in the Pacific Northwest is greater offshore. If you look at a modern mapping system, such as Google Earth, it is easier to see that this zone follows the continental shelf line, anywhere from 10 to 50 miles offshore. And the CSZ may actually be three faults that have currently merged into one. It is now believed that the Klamath Mountains and the Olympic Mountains evidence more activity, whereas our latitude is more stable. OSU has done seafloor samples about 120 miles west of our area, on the fault. The OSU/USGS report is available online (https://pubs.usgs.gov/pp/pp1661f/).
In 2018, the University of Oregon released its own study, corroborating earlier studies, and upholding greater activity in the coastlines of the Klamath and Olympic mountains (https://tinyurl.com/yy648wdh).
